There is a very big difference between lawful protest... and intimidation, thuggery and violence

Prime minister's spokesman

The firm, which has sites in Cambridgeshire and Suffolk, is in last-ditch talks seeking a further extension on the �22m loan, due to run out on Friday.

An HLS spokesman welcomed the prime minister's support and said they expected the loan extension to be approved.

But anti-vivisection campaigners from Stop Huntingdon Animal Cruelty (Shac), which organised the bank protests, insisted their stance enjoyed widespread public support.

Mr Blair's spokesman said: "There is a very big difference between lawful protest, which we support, and intimidation, thuggery and violence which we don't."

"The prime minister is very pro-science in relation to this."

Last year five cars belonging to HLS staff were set alight with home-made petrol bombs in Godmanchester, near Huntingdon.

Protesters have targeted HLS labs before

No-one was hurt but two cars were destroyed and the others extensively damaged.

The spokesman went on: "This is a legitimate industry and what's more there are thousands of jobs dependent upon it.

"We do not want to drive these industries abroad to other countries where the regulations might not be as strict."

He added that there were strong laws covering intimidation which "should be enforced".

The HLS spokesman said: "It's great to see the prime minister's extremely positive support of bio-medical research in the UK and specifically at this time.

"The legal process must be supported but when that process turns illegal, through violence and intimidation, then such protests must be condemned as robustly as possible."

Science Minister Lord Sainsbury insists life-saving medicines need to be tested

But Heather James from Shac said many people who were not even animal activists wanted to see HLS shut down.

"We speak to members of the public who are disgusted by HLS.

"We do not condone violence or breaking the law but I understand why sometimes people get frustrated when the government does nothing to close the place."

She claimed that attacks on HLS staff "were few and far between".

But she insisted the campaign to protest against banks would continue.

Branch protests

The group said there had been about 25 demonstrations at the Royal Bank of Scotland's corporate centres on Tuesday.

The bank said "appropriate measures" were in place and apologised for any disruption to customers.

Mr Blair's support came the day after science minister Lord Sainsbury said most people recognised the importance of testing life-saving medicines.

He called on the Royal Bank of Scotland to base its decisions on commercial grounds, unless it felt unable to support HLS's work.