The HPV virus causes almost all cases of cervical cancer

Around 20 patients - who were found to have early symptoms of cancer in the cervix - are being recruited to take part.

The first few have already been vaccinated, and are now undergoing weekly blood tests.

The vaccine attacks the human papilloma virus (HPV) which is present in around 90% of pre-cancerous cells - with only 1% of those cases ever developing into cancer.

It is transmitted through unprotected sex and causes almost all cases of the disease.

Experts believe that up to 50% of women may be infected with HPV during their lifetime.

Blood samples

Tests have already shown that the vaccine can kill the virus in infected tumour cells and the trial in Cardiff is aiming to establish whether or not it can destroy the virus in the cervix itself.

Over the next few months scientists at the Cancer Research Campaign's laboratories plan to test blood samples from the patients to see if the vaccine has worked.

A similar trial has begun at St Mary's Hospital in Manchester, where 24 women are taking part.

The trial there aims to boost the women's immune systems against virus.

Once the optimum dose has been decided, there will be more widespread trials to see if other vaccines can be developed which will prevent HPV infection in the first place.