Margaret and Ken Dixon

Labour and the Conservatives have continued exchanging bitter blows over the case of Margaret Dixon, the pensioner whose operation was repeatedly cancelled by the NHS.

In an exchange of letters on Thursday night, John Reid and Michael Howard traded harsh words over the conduct of the election campaign.

The Conservative leader accused Reid of "lying" about Tory health policies.

But Reid hit back, insisting he was within his rights to highlight Conservative plans for an expansion of private sector healthcare.

The spat threatened to overwhelm other political debate as both sides made every effort not to come off worst in the first full blooded battle of the general election.

The exchanges began in the Commons on Wednesday, when Howard raised the case of Mrs Dixon, saying her shoulder operation had been cancelled seven times.

Her case gained extensive press coverage on Thursday, and the Tories sought to press home their advantage later in the day with a series of press conferences and photocalls.

Howard said he had "lost count of the times doctors and nurses have told me money isn’t getting through to the frontline".

At a London media event, Howard described the Dixons as "a family that’s worked hard all their lives, paid their taxes and depended on our National Health Service".

Mrs Dixon's daughter, Lindsay, dismissed claims that her family was being used as a political pawn.

And Lindsay and her father, Ken, later travelled to Downing Street to hand deliver a letter urging the government to take action.

"This is not a game," the letter said. "This is first and foremost about getting my mum and my wife an operation to give her some quality of life."

Recognising the need not to let the Conservatives make all the running on the issue, the health secretary travelled to the Warrington hospital at the centre of the storm on Thursday afternoon.

After meeting with hospital staff and patients, Reid emerged to accuse the Conservatives of organising a "political stunt".

"I came here today because I had been contacted by staff and by patients who were angry at what they had heard yesterday from Michael Howard," said the Cabinet minister.

He said NHS workers had described the Tory leader's comments as "distasteful".

"I fully accept...that things sometimes go wrong," he told reporters.

"I don't know whether they went wrong in this case, the case of Mrs Dixon, but I'm sure the hospital management will go through the chronology of what happened and it seems it isn't quite as Mr Howard made out in the first instance."

Meanwhile, the North Cheshire Hospitals NHS Trust said the operations had been cancelled on three occasions, rather than the seven that had been suggested.

Party spokesmen continued to tour the TV studios following the visit, and the day's exchanges culminated in the late night exchange of letters.

Reid insisted he was happy to campaign on the health service, saying the government had a positive story to tell.

But Howard said the case proved that Labour's extra spending was failing to make a real difference.

The election has yet to be formally declared, but Thursday's events were a taste of how the forthcoming campaign will be fought.