A pressure group is planning to buy advertising billboards to highlight its opposition to the coalition government's controversial NHS reforms.

The charity 38 Degrees, which is campaigning against the Health and Social Care Bill, hopes to raise £150,000 to buy billboards.

The boards show an image of London GP Dr Brigid Sheppard next to the message: "Dear Mr Cameron, you're making a big mistake with the NHS. Please, please listen to us".

Many of those on the frontline of the health service have come out in force against the bill, raising concerns that reforms would increase the bureaucracy they are supposed to remove and be a form of privatisation by stealth of the NHS.

The British Medical Association, the Royal College of Nurses and the shadow cabinet expect will be joined soon by the Royal College of Physicians in opposiing the bill.

A poll revealed that nine out of 10 members of the college wanted the bill scrapped, while an extraordinary general meeting saw 80 percent vote for a total survey of members and fellows.

A spokesman for 38 Degrees said: "David Cameron is trying to ride it out. He knows his plans for the NHs are a disaster.

"But after more than a year of phoney listening exercises, aggressive spin and backroom deals, he thinks abandoning the plan now would simply be too embarassing.

"But there's one think that politicians care about more than saving face [and that's] saving their jobs. Cameron is gambling that it's best to force through the changes then hope it doesn't cost him too many votes later on.

"We can shift this calculation by proving to Cameron that the NHS is already an election issue and a losing one for his party if they refuse to listen."

The adverts will be placed in high-profile locations across London to target prospective Conservative voters. £100,000 has been raised.

The position of 38 Degrees appears to validate a letter sent by former Labour rebel Lord Owen to his former party, calling for it to campaign on the NHS in order to win re-election.

The medical magazine Pulse has revealed that a clinical commissioning group, led by the senior GP who hosted Andrew Lansley's first public speech as health secretary, has become the first in the country to call for the bill to be dropped.

Tower Hamlets CCG, led by Dr Sam Everington, has written to Cameron asking for him to abandon the bill, claiming GPs' commitment to their patients has been wrongly assumed to mean acceptance of the bill.

"We care deeply about the patients that we see every day and we believe the improvements we all want to see in the NHS can be achieved without the bureaucracy generated by the bill," the letter reads.

"Your government has interpreted our commitment to our patients as support for the bill. It is not."

The sentiment echoes that of an editorial written by Cambridgeshire GP Dr Peter Bailey, which claims GPS were "duped" into initially supporting the bill before they appreciated its true implications.

Lansley has stuck by his position that the bill will streamline and protect the NHS, while a spokesman for the Department of Health stressed that competition would "only be used to benefit patients, never as an end in itself".