The Duke of Wellington is accompanied everywhere by two black labradors. They collapse into silhouettes of helpless worship whenever he stands still, and lean adoring heads on his knee the minute he sits down. As we sit in a pale apricot drawing room enjoying a sherry before lunch, one of these dogs suddenly emits an ominous gurking sound. 'Linnet]' orders the duke, 'Go and be sick outside]'

Too late. Linnet extends her neck and ejects a trail of vomit on to the specially woven heraldic pale cream carpet.

The duke and duchess both leap to their feet and hasten from room to room in search of a shovel. 'Valerian]' the duchess's voice rings from upstairs, 'Have you found the shovel?'

'Diana?' the duke calls, 'Do you know where it is?'

There are at least a couple of servants in the kitchen (admittedly 100 yards away) who might have cleared up, but this solution would not be ducally correct. You choose to keep dogs in the house, you clear up their mess. Eventually a special shovel kept for this very purpose is located in the gun room. The duchess leads me away from the Lady Charles Room to the Print Room next door, and we sit on plump striped sofas and continue our conversation while the duke kneels and cleans up after Linnet. 'Go and chunter in your own kennel next time]' he admonishes, and Linnet fawns.

We do not eat in the formal dining room, where silver-gilt plates, candlesticks and cutlery are reflected in a Georgian mahogany table and presided over by portraits of half a dozen swarthy, frowning Wellesleys. This is a relief. Instead, we are in a pale blue private dining room, though even here the glasses are engraved with a curly 'W', and the wine - described by the duke as 'a rather ordinary claret' - is dark brown nectar. Lunch ends with home-made ice cream and a special Wellington cheese made on the estate: Stratfield Saye, near Basingstoke, in Hampshire.

This is the property bought for the duke's famous predecessor in 1817 by a grateful nation after the battle of Waterloo, won in a single day on 18 June 1815. The house, built in 1630, has a red brick facade surmounted by a turreted and chimneyed roofscape and set in a 7,000-acre park. Modest by comparison with Blenheim Palace, the seat of the Duke of Marlborough, it has a family atmosphere.

The duke has never given an interview before, and embarks upon it gingerly, as an ancestor 100 years earlier might have entered his first horseless carriage.

Conceived in Constantinople and born in Rome on 2 July 1915, Arthur Valerian Wellesley, the present Duke of Wellington, did not seem likely at birth to inherit the dukedom. But in 1943, when his uncle, the childless 6th Duke, was killed in action, he found himself the Marquess of Douro and heir to a Don Quixotian list of titles from Spain (Duke of Ciudad Rodrigo and Grandee (1st Class)), Portugal (Duque da Vitoria and Marquez de Torres Vedras; Conde de Vimeiro) and the Netherlands (Prince of Waterloo); plus several more from the United Kingdom.

His father was a diplomat, architect, and - unusually for an aristocrat - an intellectual. In 1919 the family moved back to England. 'We lived first in London and shortly after that my parents were given the Sherfield part of this estate, so that my earliest memories are of growing up in this part of the world. I've always been a passionate country dweller. My grandmother taught me about birds and at the age of eight I knew Thorburn's British Birds and Coward on Birds of the British Isles from cover to cover, and all about animals and farming.

'Then, sadly, my parents split up and that had a very clear and distinct effect on my childhood, because in those days separation or divorce was quite rare and my sister and I felt it was rather shameful. It was also trying for us, because during the holidays we had to be split half and half between them. My mother lived in the country and Vita (Sackville-West) and Harold Nicolson used to come and stay, and Yeats: many such flitted in and out of our lives.

'I went to Eton, and was happy there on the whole, though I didn't have a particularly distinguished career. Then the question was: what should happen after that? My preference would have been Sandhurst, but my parents were keen for me to go to university so I went to New College, Oxford, where I wasted a fearful amount of time and enjoyed it all a good deal. I got into debt on the racecourse and didn't do much work and took an awfully long time to get a degree. But finally, in about 1938, I went into the Blues and loved my Army career.

'War came. The mould of the very social world in which I lived was broken for ever. I had just taken over as the officer of the guard at Windsor Castle, in the Life Guards. It was envisaged that a cavalry division would go to the Middle East in 1940. One of my tasks was to go to the station at Windsor and collect the horses being sent to us from all over England.

'All these horses needed exercising, and I used to ride at least six and sometimes 10 every day, so I was absolutely whacked at the end of the day - my God] I was fit] - but I also went to parties in London after that, and being in uniform one tended to attract attention and the girls and all the rest of it, so . . . we had a great time. I used to go to the Four Hundred Club in Mayfair and beat it up quite a few nights a week and then drive back and be on parade about three hours later. In May 1940 an entire cavalry division - 20,000 horses and more men - went off to Palestine.'

On 30 December 1941 the duke was awarded the Military Cross. He is modestly evasive about this. 'All I know is that in the summer of 1941 I seemed to be very busy.' A few phone calls establish that 2nd Lt A V Wellesley, of the Household Cavalry, was awarded the MC 'for gallantry in skirmishes against the enemy'. Of the regiment, 300 strong, only six received awards at that time.

The duke goes on: 'In the winter of 1941 we were mechanised and I had to take all my old horses up into the hills where they had to be shot and left for the jackals. That was very sad: these great black horses that had taken part in all the great state occasions, finishing their days on a Judaean hill, put down in ignominious fashion.'

In early 1944 he and Diana McConnel, 22, the daughter of Maj-Gen Douglas McConnel, his commanding officer and the High Commissioner in Palestine, decided to get married. 'She was working in Intelligence in Jerusalem, in the King David Hotel - later blown up by Israeli terrorists.'

After marriage, they scarcely saw one another until the two ships in which they were returning home happened to sail side by side in convoy. 'I sent her all these loving messages in Morse code. At 6pm, as arranged, she went to the stern of her ship and I to the bows of mine and we waved across 400 yards of sea.'

After the war he returned to regimental duties. By now the Marquess of Douro, his rank and title ensured him a role on most great state occasions. When King George VI died in 1952, he commanded the Household Cavalry mounted squadron in London, on duty during the lying-in-state in Westminster Hall. 'I stood at the top of the stairs leading to the guard room. If somebody felt faint, he would signal by lifting his head slightly for a moment. The officer up there then had to come down and take his place. All day and night people passed the coffin, walking very slowly. Because your head was bent you could only see their feet shuffling past, and they looked like a river, like water flowing. That's what made people feel faint.

'In addition to my own 19 periods of 20 minutes each I substituted three times, and I take great pride in having stood 22 vigils: more than any other officer.'

The duke demonstrates the posture adopted by the officers at each corner of the black- draped coffin. His backbone and legs are rigid, head bowed, hands clasped one above the other on an imaginary sword handle. He is - the old-fashioned phrase springs irresistibly to mind - a fine figure of a man: upright and slim, with piercing blue eyes that were said to have fascinated young women in his bachelor years. He sits down again, and the dogs slump back into adoration at his feet.

'I was also the officer commanding the escort for the King's funeral procession. It was a very cold February day, and of course we were rigidly 'at the carry' and became incredibly cold because we had to go at a slow march like the foot soldiers. By the time we got to Paddington, where the coffin was put on to a train and taken to Windsor, my arm was frozen solid. I had to salute, and the only way I could move at all was by swinging it round in a great arc.'

The most satisfying job he has ever done, he says, was commanding his regiment in action against Eoka terrorists in Cyprus for two-and- a-half years from 1956; but his happiest has been since he retired from the Army in 1968, here, at the Wellington estate.

'I was able to get stuck into doing what I wanted to do: putting the estate in order and starting the country park. I felt it was tremendously important to get it moving again. My father, despite his wonderful taste, didn't realise quite how everything had changed. I don't blame him. He was an old man, and he couldn't conceive of the public walking around the house, so he just drew in his horns and lived very simply. We felt we had to revitalise and restore the house and get some income coming in; but I also genuinely felt it was something a discerning public would enjoy seeing.'

If the 1st Duke of Wellington were to walk in today, he would immediately recognise many of the rooms. Those that have been redecorated - such as the drawing room in which Linnet was sick - are comfortable and relaxing, with tapestry cushions worked by the duchess, family snapshots of their four children and many grandchildren, and signed photographs of the Royal Family.

On the walls are portraits of three 19th-century brothers known as Rough, Gruff and Elegant Stuff. 'That one, Elegant Stuff, in fact married a daughter of Lord Dexter, who's the little girl on the left there, and that's Burleigh in the background.'

There is also an enterprising young American: 'She was sister-in-law to the 1st Duke and to Napoleon, which was unbelievable.'

And everywhere, mementoes of the Iron Duke. 'We found a huge wardrobe when we came; boxes and boxes of uniforms and everything. That one is Napoleon's tunic, captured in his carriage at Waterloo.'

Most of the work that was needed has been done, and the house is now in smooth running order. 'I started early on planting trees - more than one million so far, since 1960. I've slowed up in the last 10 to 15 years.'

The duchess adds: 'The family joke is that he's created more lakes and ponds than any man since Capability Brown.'

In 1975, the duke took 550 acres of the estate to make the Wellington Country Park. 'Millions of people live completely surrounded by Basingstoke, Camberley and so on. The New Forest was under terrific pressure and I felt we had to try and produce an area where you could absorb people - horrible expression - who would hopefully learn a bit about the countryside and what makes it work. We felt this area must have lungs, where people could walk, enjoy themselves, stroll round, camp, sail, all sorts of rather quiet things.'

He piles me and the dogs into a Land-Rover and we drive off to look at it. The park gets about 120,000 visitors a year, yet never seems crowded. The duke picks up a discarded chocolate wrapper, frowning to himself. He worries about the stream drying up and the low water table. He corrects me when I call a cedar a pine tree, and then apologises for the correction, and I apologise for my ignorance. He is a country dweller; I and most of the other visitors here are townies, and it shows.

'I felt I had a responsibility to ensure that the estate continued into the future; and that task is virtually completed. I don't want to sound pompous, but I am awfully conscious that one must uphold a great name. Class in this country is breaking down a lot, you know; I'm amazed how much it has disappeared. In my sons' London offices everybody is addressed by their Christian names, and a far wider cross-section of people from all walks of life work in the different strata of the professions.

'The snobbery is now much more prevalent lower down. A century ago there was obviously more servility than today, but I remember my grandfather loved being with his keepers and grooms and got on with them frightfully well. We here have tried to maintain the best of that world - for instance, we're giving a dinner for 80 tonight for our head keeper, who's retiring after 20 years. That sort of thing is important.'

He adds endearingly, 'I hope you will call me by my Christian name.'

Perhaps because it is Valerian I cannot, as I leave, bring myself to say, 'Goodbye, Valerian.' I don't think he really expects me to. 'Goodbye,' I say, and pause, '. . . Your Grace.'

(Photograph omitted)