The Labour Party in turn is to break with past practice with the planned acceptance by Tony Blair to a private lunch invitation from Sir Richard Greenbury, chairman of the UK's most profitable high-street chain.
It coincides with reports that David Sainsbury, the grocery giant's multi-millionaire chairman and former financial backer of the now-defunct SDP, donated up to pounds 5,000 to Mr Blair's campaign for the leadership. That will irritate the Labour left, which will take it as a sign that Mr Blair is increasingly viewed as a social democrat rather than a socialist.
A Labour aide predicted that the M & S move would be the first of many approaches from business leaders who wanted to learn more about what Mr Blair stands for.
The development will be greeted by alarm by senior Tories. M & S contributions have averaged pounds 25,000 in recent years.
Sue Sadler, M & S director of corporate affairs, emphasised that the group would only make a decision after a board meeting in a few months' time. 'There will be no snap decision,' she said. 'Marks and Spencer will continue to support the Conservatives in the meantime.' But she added: 'If Labour policies are seen to be helpful to retailing in general, then it is possible we would donate money.'
While John Smith courted City institutions, acceptance of the invitation, to be confirmed on Mr Blair's return from holiday in France, represents a switch of attitude by Labour.
A spokesman insisted: 'A question of whether or not the Labour Party comes up to scratch for M & S funding is not appropriate. We are not entering a situation where a company is 'interviewing' the next prime minister.
'But Mr Blair would be pleased to meet Sir Richard to discuss matters of mutual interest. It would be churlish not to do so.'
The fact remains that Labour income from unions has declined with falling membership. Similar requests for private meetings by Sir Richard to Neil Kinnock and Mr Smith during their time as leaders were declined.
M & S is by no means the most lucrative source of Tory party income. Hanson gave pounds 115,000 last year, P & O pounds 100,000 and Forte pounds 80,000. But the switch of allegiance by such a high-profile company would give a clear sign that the business community is becoming increasingly receptive to Labour under Mr Blair's leadership.
Labour would force companies to disclose details of political donations and outlaw corporate donations that were not backed by shareholder ballots.
Leading article, page 11