Women who have cervical and womb cancers should insist their sexual partners use condoms to reduce the risk of the diseases worsening, scientists said today.

The advice followed the discovery by scientists that a chemical compound found in semen could fuel the growth of both types of cancer.

Prostaglandin - a hormone-like molecule - occurs naturally in the cells that line the female reproductive organs, but is 1,000 times more highly concentrated in semen.

"Sexually active women who are at risk of cervical or uterine [womb] cancer should encourage their partners to wear a condom to prevent increased exposure to the prostaglandins that may make their condition worse," Dr Henry Jabbour, the head of the Medical Research Council team that carried out the study, said.

However, a cancer expert said the chances of unprotected sex significantly aggravating a patient's condition was "slight".

"This is an interesting piece of laboratory research, but it has little relevance to women already diagnosed with cervical cancer in the UK because they will already be receiving appropriate anti-cancer treatment," Professor John Toy, the medical director at Cancer Research UK, said.

"The likelihood of any unprotected sex affecting the successful outcome of their treatment is considered slight. The most important thing that women can do at this time to prevent cervical cancer from developing is to go for regular cervical smear tests."

Cervical cancer is usually triggered by the human papilloma virus (HPV), which can be sexually transmitted. However, scientists believe there are other factors involved in causing the virus to develop into cancer.

Dr Jabbour said the MRC study, published in the Journal of Endocrinology and Human Reproduction, could lead to new treatments that stopped prostaglandin from affecting tumour cell growth.

There are more than 2,800 new cases of cervical cancer in the UK each year, according to Cancer Research. Although there is a higher chance of developing cervical cancer later in life, it is the second most common cancer in women under the age of 35.

There are almost 6,000 new cases of womb cancer in the UK each year. It is usually detected at an early stage, meaning treatment is often successful.