No other ITV chief is believed to make similar donations. Traditionally, TV bosses have remained politically impartial.
A consortium headed by Carlton Communications, the quoted media group chaired by Mr Green, is talking to the Office of Fair Trading about whether it should be allowed to take over the financially troubled ITN.
Mr Green, 45, paid the money to the Tories between 1 April 1991 and 30 March 1992 - a highly sensitive time during which Carlton won the London weekday commercial TV franchise.
Peter Mandelson, Labour MP for Hartlepool and the party's former communications director, said: 'It is totally unacceptable for the person heading up one of the main five TV franchises in Britain, and who may shortly be taking control of ITN, to align himself with the Conservative Party.'
Mr Mandelson added: 'I hope he will declare immediately that all such political donations by himself will cease.'
The payment was made by Mr Green's private investment company, Tangent Industries, which owns most of his pounds 40m shareholding in Carlton. Much of Tangent's income and profits are derived from the dividends it receives from Carlton and from interest on its multi- million pound cash pile.
'Tangent is a private limited company and I am not under any remit to talk about it at all,' said Mr Green. 'Carlton is a public company and makes no political contributions.' Asked when during the financial year Tangent had made the donation, he said: 'I can't recall at all.'
The Conservative Party also refused to state when it had received the money.
According to Tangent's latest report and accounts for the year ending 31 March 1992, 'the group made a donation of pounds 15,000 to the Conservative & Unionist Party'. The donation has only just been disclosed in documents filed with Companies House. Carlton TV started broadcasting operations on 1 January.
The Independent Television Commission invited bids for the ITV franchises in its controversial auction on 15 February 1991. Bids had to be in by 15 May and the franchises were awarded on 16 October of that year. The payment could thus have been made before or after Carlton won the franchise, possibly as late as the end of March 1992, when the last election was called.
The money came indirectly from Mr Green's own pocket. According to Tangent's accounts, it appears to be the first time the company has ever made any political contributions.
Carlton itself, whose report and accounts are sent to shareholders and are distributed to the City and media, goes out of its way to state that it makes no political contributions. Last year, it made donations to charity totalling pounds 363,000.
Like Carlton, none of the other big ITV companies make political contributions, though the Broadcasting Act does not prohibit such payments.
'We are very careful to be even-handed and not party political in any way,' said a spokeswoman for Central.
Thames, which lost its franchise to Carlton, made no political contributions. TV-am, another loser in the auction, also made none, even though it was run by Bruce Gyngell, the Australian who was a fervent admirer of Lady Thatcher.
Mr Green was in the forefront of opening up the auction system to competitive tender, where quality was, at least initially, of limited consideration. He enjoys close links with top Tories. His first wife's cousin is Lord Young, the former deputy chairman of the Conservative Party who was a vocal supporter of the moves to throw ITV open to competitive tender. Mr Green is now in a position to dominate the future of commercial television.
Carlton Communications also owns 20 per cent of Central, which has the ITV Midlands franchise and in turn has 20 per cent of Meridian in the south of England. Carlton also owns 20 per cent of GMTV, winner of the nationwide breakfast franchise.
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