This glittering celebration, to be compered by Gyles Brandreth, would be attended by a thousand guests drawn from the business world who would gasp at a spectacular firework display and admiringly watch films of the great man's lifetime achievements.
The Tory press couldn't stomach it: 'Tripping over his own swagger', the Evening Standard sneered. Even the Sun warned: 'There's nothing worse than blowing your own trumpet.' A few days later there was a blushing disclaimer. Portillo, it was claimed, knew nothing of the event. It was to be a surprise party. 'But do you believe that?' asked Telegraph columnist Auberon Waugh. 'Surely he must have known something.'
Modesty and self-deprecation are part of the great British character, a muted understatement that goes with the gently complementary shades of the drizzle, the tweeds and the grouse-moor. Self-aggrandisement, swagger, narcissism and plain showing-off are regarded as foreign attributes, more suited to men from abroad with oily hair and large cigars or unnecessarily handsome Italians in coloured jackets or Americans for whom the phrase 'it's sooo fabulous' greets any expression of ostentatious wealth.
The general consensus this week has been that not only was a grand bash at the Ally Pally a vulgar display but that 10 years was a little premature for celebration.
'I complete 21 years in this chair in October,' says newspaper diarist Nigel Dempster, 'and I've been very wary of celebrating it until this year. Ten years is just a flutter of the eyelids. Maybe they do things differently in Spain (Portillo's father was a veteran of the Spanish Civil War) but anyway I won't be going. I only celebrate true achievement.
'Hugh Fraser (MP and ex-husband of Lady Antonia Fraser) waited until 25 years to celebrate his time inpolitics and it led to his downfall. He had a great jamboree and the family presented a cosy loving united front which outraged people like me who knew that the truth was otherwise.'
Nor is Auberon Waugh expecting to attend. 'Certainly not,' he replied (not entirely free from vanity himself as he was speaking from Shrublands, the health farm.) 'A thousand businessmen? You must be mad. When you give a party like that you offend as many people as you please. It was a tremendously bad idea and showed bad judgement.'
Had Portillo's associates consulted the celebrity public relations man Max Clifford they would have been warned off. 'I'd have said don't do it,' says Clifford. 'No way. Even if you've achieved 10 amazing years, don't do it. If you're seen as being vain and arrogant it's very damaging. Those qualities are very bad news in this country. David Mellor made things a hundred times worse for himself by his attitude compared with Paddy Ashdown when he was in the same situation.
'Portillo's style would be farbetter suited to the American political situation where they'd be saying, 'this is one of the young pretenders'. If Oliver North was to have this party it would be a huge event and all the big stars that tie themselves to the Republicans would respond and expect to be invited. What the British love is natural humility and it's a major problem for me to get that across to the American stars that come here. If they want to be loved in this country that's what they've got to learn, humility. That's why I won't take on David Copperfield. It is a brilliant show but he's got a monster ego.'
One American in London, Lola Bubbosh, deputy editor of the Literary Review, agrees with Clifford's assessment of the difference between Britain and American attitudes towards advancing a political career. 'The kind of drive that it takes to be a politician doesn't fit in with the British character,' she argues. 'Portillo is the kind of politician who in America would simply be seen to be holding a party that is speaking to a constituency which can carry him to the top. Nobody would bat an eyelid about holding a big party like that in Washington but it does depend on your style.
'A lot of American politicians will really kill themselves not to be seen asan elite. You wouldn't just invite the chattering classes and fellow Tories. What people like is a really rich politician showing the poor folk a good time, like holding a barbecue for the south side of Chicago.'
Australian clinical psychologist Dorothy Rowe,author of The Successful Self, moved to Britain in the Sixties. Australians, she says, are half-way between the British and the Americans. 'If the rich are showing off, then that is to be decried. But on the other hand if you're invited, that's great. The British have a distaste for showing off and that's very difficult for politicians because they do show off when they get power mad.
'It was all very well for Maggie to tell us to be thrifty when she was dressed in Marks and Spencer - but as soon as she started to get a bit grand in pearls people felt it was a bit much for her to talk about frugality.'
The cross that the vain have to bear is that they are completely bemused when the public turn against them and they are hounded from public life. Did Kenneth Branagh really believe that the entire world consisted of luvvies who would applaud a man who writes his autobiography at 28? (A dual biography, of himself and his wife Emma Thompson - Ken and Em - is to be published in November.) And the sheer egomania of thinking that anyone would find someone else's sexual fantasies interesting put people off Madonna's book Sex.
One reason that the American attitude is so different to our own is that they make the mistake of believing that an unassuming manner is a signal of dimness. Not at all. Take the saint-like figure of the Princess of Wales, universally agreed to be 'Shy Di', silently suffering in a loveless marriage until she could take no more, intent on her charitable works and discreetly using others, notably her biographer Andrew Morton, to massage her public image.
On the other hand we have the extravagantly larger-than- life figure of her sister-in-law, the Duchess of York, who this week admitted to an Australian women's magazine that her 'massive ego' had led to her downfall.
After Robert Maxwell's death, publishers released from the threat of legal action rushed out books which consisted of little more than a series of dinner party anecdotes about his ego and vanity. Maxwell, more than anyone else, was a monument to all those qualities that just aren't English and just aren't on - such as (and say this in a hushed whisper) hair dyeing. The publisher employed a barber called George who was on call 24 hours a day to be summoned, by Concorde, to apply a tint whenever the publisher's roots were showing.
Perhaps Gyles Brandreth was called on by Portillo's aides in the light of his experience compering the birthday parties Maxwell would hold every summer at his stately home Headington Hall for 'a thousand or so' of his closest friend. According to Brandreth, Maxwell would wear a small lapel mike so that his amplified voice could be heard and enjoyed in every room.
Yet despite our national disaffection with show and swagger, the vanity industry is a growth area. Books pages are littered with advertisements for vanity presses - publishers who promise that they are avidly seeking new authors and then demand that you pay to have a thousand bound volumes of your memoirs stacked up, unsold, in your garage.
Every year Who's Who, which lists 29,000 of the good and the great, receives a 'certain number' of letters from the would-be distinguished, demanding to know why they haven't been included. 'Or sometimes their friends write in for them,' says a spokeswoman for the publishers who themselves are living exemplars of English modesty, never known by name outside the company. 'It's not necessarily something we frown on as people do sometimes slip through our nets.'
But what do you do if you can't get into Who's Who? In 1988 Debrett's launched People of Today, a biographical reference volume for those not quite distinguished enough to make it, a kind of life's B-list.
'If I'm going to be objective, I'd say that Who's Who covers the establishment better than we do,' says Jonathan Parker, editor in chief. 'We would put in section editors of newspapers and a senior partner with an accountancy firm. The difference is that unlike Who's Who we take them out when they retire or are no longer in the spotlight.'
People of Today sends out 3,000 invitations a year and receives between 1,500 and 2,000 forms back plus an additional 125 refusals. The rest, presumably, go in the bin.
But who wants to read about Mr Stubbins, executive in charge of noticeboards and paper clips, at pounds 97.50 a volume? 'It's bought by libraries and companies,' Parker says, 'and the people who are in it. There's a certain amount of vanity sales in the publication.'
As Michael Portillo licks his wounds this weekend, he might consider that modesty, as Dorothy Rowe believes, can be itself just another kind of face. 'Pride is the deadliest of the seven deadly sins and people dislike it only because they believe it comes before a fall. The distaste for show is part of the tradition of wearing old clothes among the upper classes. I don't know how they get those old Burberrys in the first place.'
To the outsider the English reverence for self-effacement can seem like a subtle and impenetrable code. A private dinner rather than a grand bash can be the ultimate chic, the most desperately sought after social invitation. Those who detest the vice of vanity may be themselves suffering from another - snobbery.
ARE YOU VAIN?
1) On receiving a form asking for your biographical details for a reference work of notable people, would you: a) Fill it out at once, including swimming certificates and O-level grades, then bike it back by return. b) Bin it - feeling secretly satisfied at being asked. c) Write back, explaining you are deeply honoured, but feel your modest achievements are just not worthy of inclusion.
2) Celebrating 10 years in the same job, would you: a) Hire Stringfellows and fax invites to Madonna, Arnie, Liz Taylor and Lady Thatcher. b) Bring a bottle of sparkling wine and some Twiglets in to work and hold a 15 minute impromptu party during the lunch break. c) Try to keep the anniversary secret. They might make you redundant when they realise you've been there that long.
3) You discover that your mother's maiden name was Major. On consulting a genealogist you find you are indeed related. Would you: a) Commission a coat of arms and send it to the Prime Minister, find a Downing Street in your area and make an offer on No 10. b) Invite his brother Terry round to tea. c) Start investigating the possibility that you were adopted.
If you score mainly a) how vulgar] simmer down at once; mainly b) you sometimes blow your own trumpet just a bit too loudly; mainly c) you are charmingly modest; very British.