Murphy vehicles, often a bit battered, attend an ever-increasing number of roadworks (filling holes in the Tarmac, installing and repairing drains, mains and cables - contracts for the public utilities). Their crews, speeding from site to site, often address one another in the accents of south-west Ireland. But the Murphy profile, high on the highway, is lower elsewhere.
J Murphy & Sons Ltd is a secretive outfit, employing about 2,000 and with an annual turnover some say is now approaching pounds 200m. It is headed by a publicity-shy Irish septuagenarian, John Murphy, whose personal fortune is said to be well in excess of pounds 100m. Hard facts are as elusive as Mr Murphy, who recently boasted to an acquaintance: 'No one has ever managed to take a snap of me.'
To be fabulously rich and mysterious is a formidable achievement. The late Howard Hughes mastered it by locking himself away in a Las Vegas hotel suite. At 71, however, Mr Murphy eschews such extremes. 'On a Saturday morning he'll turn up at one of the Murphy sites and have brekkie with the workers, and show the slower ones the best way to handle a shovel,' says another acquaintance. He frequently appears at the Irish Club in Eaton Square. He mixes easily with London's Irish community which sees him as a benefactor. Yet, to the wider community, he is the Great Murphy Mystery.
Highview House - Murphy's London headquarters - is in an unglamorous part of Kentish Town, between a railway bridge and a popular music venue, the Forum club (landlord, John Murphy). At a gatehouse, barriers rise and fall with dizzying frequency, as the dark- green fleet races in for supplies and races out again.
The second checkpoint is across a courtyard with young trees and plants along its walls, a rus in urbe that contrasts with the dust, fumes and sweat of Murphy's adjoining area. Highview House is a modern business citadel: one-way windows, and a marble reception desk resembling a bunker. In the courtyard are two white beehives - apparently a Murphy metaphor; worker bees swarming as urgently as the green vans at the gatehouse. The hives, it seems, are a gift from a Murphy friend in Ireland who preferred 'Hive-view' to 'Highview'.
Most of Mr Murphy's friends in Ireland and Britain insist on anonymity. They describe the millionaire variously as 'a great man', 'a humble man', and (in the words of an Irish priest in Camden) 'one of nature's gentlemen'. But in the gush of praise, no one seems to have got the measure of John Murphy. 'I'd say he was between 5ft 9in and 5ft 10in,' says a London-based Irish journalist. 'He's not a whisker short of 6ft 2in,' declares a businessman in Port Laoise, Ireland. 'I wouldn't put him above 5ft 8in,' says George Henderson, an official of the TGWU who has had dealings with Mr Murphy over the years.
The company has a press officer who does not talk to the press, other than to forbid inquiries. Fulfilling this odd role is a Mr O'Connor, who refuses to reveal even his first name, saying brusquely on the phone: 'We don't want people turning up on our doorstep. This is absolute bullshit. It's got to stop.'
Why does John Murphy keep them guessing? The answer may lie in the past.
As a youth, it is said, he set out on foot from his father's small Kerry farm at Cahirciveen to seek work in London. Hitch- hiking much of the way across Ireland, he caught the Dublin boat - and rode the wave's crest for most of the ensuing years.
He and his brother Joe eventually formed separate building and engineering companies, the latter painting his vehicles grey (they are known in the trade as 'the green Murphy' and 'the grey Murphy'). They flourished on post-war reconstruction, tendering for large-scale contracts particularly in pipe-laying, fulfilling them quickly and proving adept at tapping into Ireland's large labour pool.
By the building boom of the early Seventies, J Murphy & Sons Ltd was handling major business for British Rail, doing round-the-clock repair work for the Greater London Council, laying land pipelines for North Sea oil and gas, and being referred to as a 'big-league company'. 'John used to say that if you don't work hard you don't survive,' says a Murphy friend in Ireland. 'He's a simple man whose hobby is work. And when he gets tired he works again.'
He saved hard, too. 'He didn't go in for luxuries, even when he could afford them,' the friend says. 'When I asked him why he didn't buy a racehorse or two, he said: 'Horses have to eat, whether they win or lose.' '
But the Seventies also brought trouble. In 1972, Murphy sold 75 per cent of the company's equity to the London and Northern Securities Group for pounds 6.75m. Most of the remaining 25 per cent remained in the hands of the Murphy family and trusts. Two years later, the Inland Revenue mounted a major campaign against tax evasion through the system of employment in the building industry known as 'the lump'.
About 400,000 workers were said to be in the system, under which self-employed labourers, often operating in gangs, hired themselves out to the highest bidder. Not all evaded tax, but those who did were reported to be costing the Exchequer up to pounds 100m a year.
Among those targeted by the Fraud Squad, the Flying Squad and the Regional Crime Squad was J Murphy & Sons Ltd - though not John Murphy himself. In 1976, after a prolonged legal battle, the company was fined pounds 750,000. Two directors and the company secretary were jailed for three years and fined pounds 10,000. Another employee was jailed and fined, and four more were given suspended sentences and fined. The judge said: 'I find it difficult to speak with moderation when a large, well-known, highly efficient and hitherto respectable company engages in a gigantic swindle of this kind.'
It was a severe blow. But John Murphy was uncrushed. In 1977 he bought back his 75 per cent share for pounds 5.03m through Drilton, a subsidiary of an Isle of Man investment company wholly owned by Murphy family interests. Since then, Murphy's has spread into different ventures, including property, via another Murphy firm, Folgate Estates, a demolition company in Scotland, a readymix-concrete firm in London's Park Royal, a shipping company in Greece, hotels in Ireland, and an airport in Kerry. Four years ago, it completed the mile-long Stansted airport tunnel, using a giant boring machine brought in from Singapore. Murphy's has also won contracts in the Middle East. John Murphy owns 18 companies in Britain under different names.
To keep track of his empire, he maintains a punishing pace. 'I'll tell you a typical day for him,' says a friend. 'He could drive to Heathrow, fly to Glasgow, then to Dublin, then drive to Limerick and back to Dublin, and return to London in the same night. He never stops. If there was a ladder up to the fourth floor of a building, he would be up it in seconds.' For all this, he is paid (according to information filed in Companies House) a salary of pounds 350,000, compared with pounds 90,000 earned by his next highest-paid executive.
Eight years ago, Mr Murphy ended a period of widowhood by remarrying. London acquaintances say he now takes some time off for golf and dancing with his 'young and attractive Irish wife', a former nurse.
Murphy employees can be fiercely loyal. A business rival says of the elder Murphy: 'When you look at the people running his company, it's remarkable how many are the sons and daughters of those who started with him.' Another rival, Bernard McNicholas, of McNicholas Engineering Ltd, a family firm with origins in Co Mayo, says: 'I rate him very highly - a brilliant businessman, but quiet socially.'
A third admirer says many Murphy men, having learnt from him the virtue of hard work, later went on to establish their own businesses. According to Irish sources in London, among those who benefited is Dick Spring, Ireland's foreign minister. As a student, Mr Spring (also a Kerryman) was offered work in London by Mr Murphy, who told him: 'It's pounds 20 at street level, pounds 25 a bit lower down, and pounds 50 if you work in the sewers.' Mr Spring chose the sewers, and has never looked back.
Nor has the company. In 1992, when similar firms were reeling from the recession, J Murphy & Sons made a pounds 13.2m profit on a turnover of pounds 140m.
Accidents do happen, however. Last year the company was fined a total of pounds 160,000, plus pounds 28,000 costs, for safety breaches that caused the electrocution of a worker. Despite such setbacks, the Murphy fleet, though battered, remains unbowed.