He then put down the phone with a gingerness that suggested the receiver was red-hot.
'There's so much back-biting going on at the moment,' he said, nodding at his phone. 'You know, this can be a rough business.'
The Financial Times has estimated that last year Power's empire turned over pounds 8m. 'Rough business' indeed.
Such money ought to be enough, you might have thought, to employ someone to open the door of your office building for you. But Power prefers to do that sort of thing for himself. Next to the closed-circuit television nailed to his office wall ('that's my alley-way,' he says proprietorially, pointing to the screen) is a video entry-phone monitor. Throughout this interview he answered it diligently.
'Who are you?' he would say into it, swivelling round in his office chair. 'Oh, all right, come in.'
Power now has under his wing the five most fashionable concert halls in London. He was the man who rescued the Reading Festival from bankruptcy in 1988 and made it profitable. Last year he staged the Madness reunion concerts, which attracted more than 50,000 people. This summer he has huge festivals to organise in Stratford-upon- Avon; Paris; Boston, Massachusetts; and Finsbury Park. What with all that and answering the door as well, it is no surprise he has the crumpled look of Phil Collins after a lengthy night out.
'When I first started,' he said, allowing in a long-haired man carrying a guitar, 'I thought I could run a club in the evenings as a hobby.'
If, like Power, you were ever tempted to stage rock concerts as a hobby, his experience might be instructive. He arrived in England from Dublin in the early Seventies with no more than the price of a concert ticket in his trousers. After spending much of the decade building up a chain of furniture stores, he thought, aged 35, that it would be fun to turn one of his shops into a country music club. In 1982 he opened the Mean Fiddler - 'that's mean as in the Irish for good,' he explained. 'Not tight-fisted.' It was in Harlesden, one of the hardest parts of north London.
'I had a lot of trouble when I opened from lads who saw the place as an after- hours drinking den,' he said. 'They were disappointed when I turned them away at the door. I had my car windows smashed up all the time by people I wouldn't let in. It was an old Beetle. In the end I was just keeping it to be smashed up. I guess it was healthier than smashing faces.'
He persevered, changed musical policy when he discovered that few people shared his taste for old-fashioned country and western, and turned the Fiddler into a nice little earner.
'We improved the standards of concert-going,' he said. 'We made it a nice place to watch a band. We put wine behind the bar. Proper wine, not a slug from a two-litre bottle. Mind you, nobody buys it in Harlesden.'
From there, after taking on a night- club under the motorway in west London he named Subterrania ('the local heavies there were much more sinister, they'd pull up alongside you in an expensive car, wind down the electric windows and just stare at you for five minutes') he bought a faded music hall at Clapham Junction, south London, called the Grand.
The Power plan to turn it into a rock concert hall was a fraught venture. Once again it was the locals who caused him problems. This time they didn't threaten him physically, they complained to Wandsworth Council.
'The trouble was, the local councillors objected to my licence applications because they relied on these people for votes, and so took their complaints seriously,' Power moaned, clearly puzzled by the workings of democracy. 'When I bought the Grand in 1990, the locals were worried that proximity to a concert hall would reduce the value of their nice, expensive flats. Funnily enough one of the main objectors was that geezer from the pop group Dead or Alive. But in the end it was the recession that did the reducing.'
To meet residents' objections, Power cotton-wooled the Grand with so much expensive sound-deadening that he could re-enact the Gulf War in the place and passers-by would think someone had dropped a box of pins inside. At the end of this month, it finally opens as a fully functioning concert hall, after three years of legal activity.
'I've been to that many licensing hearings,' Power said. 'I'm a bit confused as to what licences I've got.'
As Power was building up his business (he bought the slick Jazz Cafe in Camden Town in 1992 from the official receivers), not far from his headquarters an entrepreneur called Ollie Smith was enjoying a reputation as the manager of the country's favourite rock venue. His Town & Country Club in Kentish Town played host to nearly 200 sell-out concerts a year, by everyone from Jesus Jones to Tom Jones.
But it wasn't just the ticket sales that made Smith's a profitable enterprise. The T & C was Scottish and Newcastle Breweries' largest outlet in the country (and it's not even in Tyneside). The cash-flow generated by its bars was the envy of any businessman.
Despite his success, last autumn Smith was told that his lease would not be extended by the building's owner, John Murphy. Murphy, a shy building millionaire, refused to explain why. Sensing demolition of the building was in Murphy's mind, Smith launched a campaign to save the place. Suggs of Madness was photographed holding a placard outside. Keith Richards said it was a national disgrace, man.
Then, two weeks ago, with Smith looking for new premises and concert- goers mourning the loss of their favourite haunt, it was announced that Vince Power was taking over.
Smith thinks Power was discussing the deal months ago. 'Retrospectively, the campaign to keep the club open was a waste of everybody's efforts. I wouldn't have asked them if I'd known. It's embarrassing.'
There was much talk in the music papers of the Murphia in action: Irish businessmen looking after their own.
'We always had a good relationship with Vince,' said Smith, who isn't Irish. 'There was a feeling of us together against the rest of the world. I think it's a shame in a town where there is so little infrastructure for music that he felt necessary to scramble over us.'
At the mention of the Town & Country and Ollie Smith, Power smiled wryly.
'Basically, it's over and finished,' he said. 'Ollie Smith is just trying to continue a war that doesn't exist. He's just bitter, which I suppose you can understand. All I can say is that music lovers should be pleased. Things will be much better there.'
Despite all the 'rough business' over the T & C, the acquisition of the place is not the end of Power's plans. He has another concert hall in mind, as well as an idea for opening up Mean Fiddlers across Britain and France.
'I have lots of ideas,' he said. 'Fortunately a lot of them never see the light of day.'
According to another concert promoter, Power is 'a very good operator, but that doesn't mean he should rule the world. Monopolies are very dangerous.'
'There is no way I could use my situation as a monopoly,' said Power. 'There are 300 concert venues in London. I just happen to have five of the best. Perhaps that is not a coincidence.'
And with that he looked at his watch, politely terminated the interview, and, after opening the door for me, returned to his full-time hobby.