The new Mr Big of modern art?

He is the Charles Saatchi of the North, the self-made millionaire credited with the most important private contemporary art collection in Britain after the advertising guru himself.

Tomorrow, Frank Cohen is inviting curious Londoners to see highlights of a collection that until now only his friends and a few art-lovers in Manchester have had the opportunity to view. In the splendour of a Grade I-listed Georgian townhouse, nearly 30 works by artists including the Chapman brothers and Luc Tuymans, the highly influential Belgian who is the subject of a summer show at Tate Modern, are going on show. There is a video installation by Matt Collishaw, Tracey Emin's ex-boyfriend, and sculptures by Paul McCarthy, the artist who had two giant inflatables bobbing around outside the Tate Modern last year.

"It's an incredibly fine collection," said Anthony McNerney, a specialist in post-war and contemporary art at Christie's who agreed to help Mr Cohen hang the show. "He's very knowledgeable and extremely well-read about contemporary art. He knows a lot of the dealers and listens to them, and he knows a great number of artists and talks to them. He's a consummate collector."

Frank Cohen, 60, lives in an affluent part of Cheshire with an Emin, a Grayson Perry pot and a Lowry among others, but only one piece from his home - a McCarthy - has made it to London. Most of his 1,000-strong collection, which is stored in the Midlands, is unsuitable for the ornate grandeur of the Georgian house that has been lent for the occasion by the bank, EFG.

But Mr Cohen is eager to know what the critics will make of this first glimpse of his private passion, art accumulated over 30 years and funded with the proceeds of a DIY/home improvement business he built from scratch and sold in 1997.

"I want to know what they will write about me. I'd like to know what the critics say," he said yesterday, as he swirled around the building, answering his mobile phone between making improvements to the hang.

He started young, collecting cigarette cards and coins, before moving into art three decades ago, starting with modern British painters and sculptors such as L S Lowry, Stanley Spencer, Barbara Hepworth and Eduardo Paolozzi.

"Then that period left me because the artists were dying and the dealers were dead and the contemporary art world took over from there," he said.

He has, in fact, displayed a few of his contemporary works before, to benefit a friend who runs a small gallery in Manchester. But, he noted, no critics deigned to take a look at that.

"When you live in Manchester, no one knows you exist," he said. "They're quite a close-knit community down here. I could have 50,000 pieces in my collection, but I'd still only be a collector."

Now he feels like a film star but he claims he does not care whether the critics like what they see or not. "I couldn't care less," he said. "I do what I do. I'm not the kind of person who's going to cry my eyes out if they say they don't like it."

The interest is immense with a cavalcade of international journalists passing through the not-quite complete show yesterday for a preview.

Mr Cohen's display is part of a giant initiative called Art Fortnight, in which the capital's auction houses and private and public art galleries are co-operating to promote London's pre-eminence in the art market.

He is taking part after being invited by the writer and Art Fortnight organiser, Meredith Etherington-Smith. It is, he adds, "a great opportunity". It is also, perhaps, a taster of the much bigger permanent gallery he intends to open in the heart of Manchester next year, a tantalising advertisement worthy of Charles Saatchi.

But Saatchi is the one subject Frank Cohen will not discuss. They are virtually the same age and both built a business empire instead of pursuing higher education. Like Saatchi, Cohen is a perfectionist, moving sculptures to left and right for maximum impact, railing at the chandeliers spoiling the view of a colourful Frank Ackerman. Where they differ is in Frank Cohen's chattiness. He is as voluble as Saatchi is reticent about his art. Mr Cohen makes clear he believes there is nothing to be gained by discussing Saatchi - even though the more famous collector has already popped in to take a look.

Critics will finally be able to compare their two collections properly when Frank Cohen opens his Manchester gallery. It will cover 25,000 sq ft in the heart of the city and will have space for up to 200 paintings and sculptures, enabling a proper display of contemporary Germans, such as Andrea Slominski and Tobias Rehberger, young Brits including this year's Turner prize nominee Yinka Shonibare, and Americans, such as his current favourite, Richard Prince.

McNerney said: "He's always spotting artists and championing young artists so there are some unsung heroes of contemporary art in his collection that will probably be the most exciting things to see."

Yet Mr Cohen has just one assistant and one conservator to help him with his collecting. His art is "pretty much" what he does these days, apart from the odd property deal.

He is proud of what he has. Looking around the exhibition yesterday, he almost bounced with excitement. "It looks good, doesn't it?" he said.

The Frank Cohen collection is on show with the Neil Kaplan collection of Rembrandt etchings at 3 Grafton Street, W1, on weekdays from tomorrow until 2 July.