A breast cancer surgeon turned MP is calling on fellow politicians to back a bill which will unlock potential new treatments for thousands of patients.

The SNP's Philippa Whitford is backing a campaign to change the law in a way which will breakdown barriers that can currently prevent cheap, existing drugs being given to patients with a range of conditions.

Doctors and researchers sometimes find treatments licensed for one health problem benefit patients with an entirely different condition. However, when these medicines are no longer covered by patents and are sold quite cheaply, there is little incentive for drug companies to apply for them to be licensed for a different use.

This problem is affecting treatments for conditions as common as breast cancer and multiple sclerosis.

The bill, facing its second reading in Westminster, creates a duty on the government to step in and act to ensure such drugs are assessed and, where appropriate, made available to patients.

At the moment doctors prescribing drugs off licence have to sign a form which makes them personally responsible for any adverse incidents.

Dr Whitford, the MP for Central Ayrshire, revealed as a breast cancer surgeon she had to sign such a form whenever she used a blue dye to guide her while removing lymph nodes - even though using the dye was considered best practice. She explained: "Eventually I said to the health board I am not willing to put my house on a piece of paper when if I didn't do this I would be breaking the guidelines."

Dr Whitford said she was also involved in looking at whether a treatment for osteoporosis could help prevent breast cancer spreading to the bones. In hospital where specialists know the latest advances and work in a team, she said, prescribing off licence was less problematic - but when it came to GPs administering the medicines it could run into problems as the doctor could not look up the recommended dose and may feel isolated.

She said: "It seems to me silly to have a system where you have got a drug that has been proven for something, that has been around for 20 years so you know the safety profile and it is cheaper than chips, but for the lack of sorting out the paperwork you leave it on the shelf."

The off-patent drugs bill has already been backed by 40 clinicians across the UK.

Professor Siddharthan Chandran, director of the Edinburgh Centre for Regenerative Medicine - which is currently leading trials using off patent drugs in patients with MS, has added his voice to the campaign.

Professor Chandran said the bill would increase the chances of treatment for people with really tough diseases. He continued: "I strongly believe the UK should be leading on this and Scotland particularly for diseases like MS."