The tobacco industry is one of the big backers of the Tory Party election fund, and Ian Greer Associates - at the centre of the cash-for-questions scandal - acted as one of the lobbyists in the past.
The deal threatens to reopen the controversy over the relationship between the Conservative Party and the tobacco barons during the election.
The deal, allowing the industry to continue putting around 600 additives in tobacco products, was slipped out in a written Commons answer hours before the House rose on Thursday night for the election recess, although officials said it had been signed on 7 March.
"The additives can release the nicotine in the tobacco which makes it more easily absorbable. You can argue that some of these additives are designed to keep the smoker hooked," said a spokeswoman for Ash, the anti- smoking campaign.
"It is another example of the cosy relationship between the Government and the industry, which is a significant donor to Tory funds. This is probably the pay-off."
A Department of Health spokeswoman said the additives were to increase flavour to enable the tar levels to be lowered. But Ash said: "There are no real health gains from smoking lower tar cigarettes because smokers tend to inhale more deeply. It is counter-productive."
Chris Smith, Labour spokesman on health, is committed to banning tobacco advertising as part of Labour's campaign to bring in tougher public health measures and curb the rise in teenage smoking. "The Conservatives must come clean about their relationship with the tobacco industry and how much money they receive from them," he said.
The former prime minister, Margaret Thatcher, was paid around pounds 500,000 a year as a consultant for Philip Morris. Marlboro also paid $1m to subsidise an 800-guest, pounds 15,000-a-table 70th birthday party in Washington DC. The Thatcher Foundation raised pounds 1.5m.
Mr Smith wrote to Brian Mawhinney, the Tory Party Chairman, and a former health minister, this week calling for him to disclose details of the donations from the tobacco industry to party funds.
It followed the publication of the cross-party Commons Public Accounts Committee report, showing that it was "dismayed by the rise in teenage smoking", in breach of the targets set in the Government white paper, The Health of the Nation. The committee noted that the Government had failed to reach its 1994 target of six per cent of 11-15-year-olds smoking, and it had seen a rise in the proportion of smokers in this age group to 12 per cent.
The Tobacco Manufacturers' Association was unable to provide details of the additives last night. "There is nobody here that can explain that," said a spokeswoman.