He raised the party political stakes in the continuing controversy over whether ministers are in conflict with the Government's 'back to basics' policy, by turning the tables on Labour smears, which he said were 'the hallmark of political cowardice' and the 'trademark of the Opposition'.
Within an hour of the exchanges in the House of Commons, Conservative Central Office was ready with a detailed briefing on what it claimed were a series of baseless Labour 'smears' dating back to the controversy over the Bank of Credit and Commerce International collapse in 1991.
Labour swiftly countered by gleefully declaring that the Prime Minister's move showed how 'desperate' the Tories were in the face of the party's attacks - which were renewed in the Commons yesterday by John Smith, the Labour leader - on the 'hypocrisy and deceit which characterises everything they have said about tax'.
A senior Tory official acknowledged under questioning that the recent ministerial resignations and scandals had not been exploited by Labour politicians.
But he issued a list of seven separate 'smears', ranging from a claim by Clive Soley, the Labour MP for Hammersmith, that Michael Heseltine, President of the Board of Trade, had received pounds 7m from the Saudi royal family - which Mr Soley refused to repeat outside the Commons and was the subject of a newspaper apology, to the more run-of-the-mill Labour charge during the Monmouth by-election campaign that the Government was intent on 'privatising' the National Health Service.
Others included: the claim that the Tories sold honours; the Jennifer's ear party politicial broadcast on the NHS; the claim that Wandsworth council had gerrymandered, despite being cleared of the charge by the District Auditor; and the implication on Monday by Robin Cook, Labour's trade and industry spokesman, that he did not believe the Prime Minister's testimony to the Scott inquiry.
The levelling of the charge by Mr Major came in an answer to David Winnick, Labour MP for Walsall North, who spoke of 'the amount of financial sleaze in this country arising from government policies and attitudes'.
Mr Major said that he agreed 'entirely about the necessity for integrity in public life', but then he startled MPs on both sides of the House by adding that it was also necessary for Labour to look 'at their own colleagues who spread smear and innuendo on a week-by-week basis with complete disregard for the truth'.
Central Office produced a quotation from Mr Smith's R H Tawney memorial lecture last year, in which he had stressed that 'politics should be a moral activity' and suggested the 'smears' contrasted with that aspiration.
Yesterday, Mr Smith twice challenged Mr Major to say whether he had been alerted to the fact that the freezing of tax allowances would mean 400,000 more people would pay tax in the 1994-95 financial year. He urged the Prime minister to recall 'the repeated promises you made to the British people that you would not increase income tax', along with VAT and national insurance.
Mr Major retorted that it was clear that the 'standard rates of tax under this party have dropped dramatically since your party was in government'.