The paper aims to have an initial print run of 100,000 for its single afternoon edition run.
Tonight's managing director, Geoff Speggals, says he regards the new paper as complimentary to the Standard, London's only paid-for evening newspaper, rather than as a competitor.
But a counter-offensive from Associated Newspapers, publisher of the Evening Standard, can not be ruled out.
Publicly at least, Associated, part of Daily Mail and General Trust, which also publishes free newspapers, appears unruffled by the prospect of a new entrant to the evening market. 'Why should we worry any more about this than if somebody was launching a free-sheet called Hounslow Tonight?' said Anthony Hilton, the Evening Standard's managing director.
He argues that the new paper will not have the fundamental value of most free newspapers - a targeted, home-delivered product that can offer advertisers a specific audience at cheap rates.
'The Standard has had competition from free newspapers for 15 years, and I'm yet to be convinced that this one is any different. It's going to have around 15 journalists. We have 250. It's got four vans. We have 225. A new Evening Standard this is not,' Mr Hilton said.
Privately though, sources at Associated suggest that there has been serious thinking about the new project and its likely effect on the Standard. There are rumours that a sophisticated plan to deal with Tonight will be hastily put into operation if it begins to look like a threat to the Standard's monopoly position.
'We're not aware that Associated is doing anything specific, but it may have something up its sleeve,' Mr Speggals said, speaking from the paper's offices in Southwark Bridge Road, just south of the Thames.
Tonight will kick off with 16 pages of news, features, sport and advertising. The paper will be edited by Peter Grimsditch, who has worked on a series of tabloid newspapers. It will be staffed by a dozen or so journalists, relying mainly on Press Association, the news agency, for its news coverage.
'We will be as reasonably up-to-date as we can be, given our intention to have the paper on the streets for the period between four and seven o'clock in the afternoon,' Mr Speggals said.
Apparently, the paper will be handed out by 'distinctively dressed' people at 20 to 30 sites around the area enclosed by London Underground's Circle Line.
It is to be pitched at the middle market and its politics will be 'as neutral as they can be while supporting the London commuter,' Mr Speggals said.
He declined to say how the paper is being funded initially, although Mr Clee is reported to be investing anything between pounds 200,000 and pounds 1m of his own money to get it off the ground.
Mr Clee was formerly a strategy planner at Philips, the Dutch electronics group, where he teamed up with David Ross, the company's financial controller, to buy Philips's tumble- dryer factory in Halifax.
The deal, a management buy-out, was financed by the American bank Bankers Trust, which lent the money to the two entrepreneurs without being given a stake in the equity. The deal appears to have been most favourable for the purchasers: last year's accounts showed profits to be up 72 per cent at pounds 5m.
Mr Clee comes into the venture with a strong conviction, backed by market research, that London should have and can sustain a free newspaper alongside the Evening Standard.
The publishing company running the new project is callled Mermaid Enterprises. Its sole shareholder, with 99,998 shares, is Mr Clee.