Labour faced multiple accusations of foul play from the Conservatives over their use of the NHS as the first full week of campaigning began.
The Tories said Labour had sent cancer scare leaflets to patients, canvassed support from GPs using their work email addresses and broken Cabinet Office guidance on the launch of their manifesto.
This morning's manifesto event took place in a newly-completed NHS hospital in Birmingham, a move Gordon Brown insisted was legitimate because it was owned by the construction firm rather than the local trust.
Shadow defence secretary Liam Fox told a hastily-arranged press conference in central London this afternoon that Labour chiefs had "exploited a loophole" to lay claim to what he called "Britain's NHS, not Labour's NHS".
And shadow children's secretary Michael Gove said this and other moves were "the next step in Labour's cynical exploitation of our NHS for narrow partisan advantage".
The pair repeated newspaper allegations made yesterday about Labour 'microtargeting', in which voters with specific concerns are sent literature relating to the issues which affect them most.
It was claimed that Labour was sending personalised Labour 'scare cards' to patients, despite previous denials that they were targeting material at people suffering a medical condition.
The Tories produced a Labour document sent to candidates which said that mailings could be personalised based on a number of criteria - including approximate household income, tenure, families with children and "age or life stage".
And they said a Labour party development officer had been canvassing political support by contacting GPs with their work email addresses.
"The Labour party are targeting GPs by sending unsolicited emails pressurising them to sign a press release in support of a set of vague promises," senior Royal College of Physicians adviser Jonathan Steel said. "This is an appalling tactic."
The Liberal Democrat health spokesman, Norman Lamb, accused the Conservatives of "double standards" on the NHS, however.
"Only last week David Cameron was happy to go campaigning in Kingston hospital, but suddenly the Conservatives are saying it's unfair for parties to use the NHS in this way," he commented.
"The pettiness of the Conservatives' response is beyond belief. People will not be impressed with a party that has so little to say about Labour's legacy of failure."