The government last night denied having a secret plan to target NHS hospital closures on constituencies where the least damage would be done to Labour's chances of winning the next election.

Advisers to Patricia Hewitt, the health secretary, confirmed her department had drawn up a "heat map" showing areas where there is strong public unrest about proposals to downgrade A&E departments and close facilities. But they rejected suggestions from opposition parties that Labour is using the map to avoid NHS cuts in sensitive marginal seats.

A leaked email showed that proposals to circulate the map to senior Labour figures were discussed at a meeting in July between Ms Hewitt, the Labour chair Hazel Blears, and Downing Street political advisers. Rosie Winterton, the health minister, said yesterday that it was appropriate for Ms Blears to be kept informed about NHS reforms and there was "nothing sinister" about the meeting.

The row came as Unison, the public service union, announced plans for a 24-hour strike next Friday, in protest at the government's plans to privatise NHS Logistics, the health service's supply agency. It also followed the disclosure in the Guardian on Wednesday of plans for widespread "reconfiguration" of the NHS in England. David Nicholson, the incoming chief executive, said many A&E departments may have to be closed or downgraded when care for serious accident victims switches to regional centres for major trauma. Maternity and paediatric care may also be centred in fewer hospitals.

Andrew Lansley, the shadow health secretary, said Ms Hewitt's decision to discuss the map with Ms Blears and a party representative was outrageous. He asked: "What are clinical staff in the NHS to think if these difficult decisions are, in fact, being manipulated at the highest level for political advantage by Labour ministers?"

There were no cuts in Ms Blears' Salford constituency, but the NHS decided yesterday to downgrade the A&E department in nearby Rochdale, where Labour lost the seat to the Liberal Democrats at the last election. A spokesman for NHS Northwest said: "The proposals were made some two years ago and local consultation on them finished back in May. That is long before any alleged secret meeting by Labour ministers took place."