Vital medical research is under threat in Britain because ferry companies and airlines are bowing to pressure from animal rights activists and refusing to carry animals destined for laboratory testing, scientists and drugmakers said on Wednesday.

Researchers said all ferry companies operating routes into Britain had banned the import of mice, rats and other animals used in research labs to explore experimental new drugs.

Threats to the carriage of these animals will slow down the progress of essential and life-saving biomedical research, said scientists from the Medical Research Council, the Association of the British Pharmaceutical Industry, the Association of Medical Research Charities and others.

While the vast majority of animals used for research in Britain are bred locally there are certain programmes where groups from different parts of the world find it essential to share specific strains of animals, the scientists said.

It takes a long time to breed these animals and if their transport is stopped then researchers will have to recreate them, requiring the unnecessary use of many more animals over successive generations, they said in a joint statement.

With strict rules in place to ensure humane transport, international animal transit mostly relies on airlines, partly because flying means shorter travel times.

In Britain, however, ferries have been increasingly relied upon since previous campaigns by animal rights activists prompted airlines and airports to withdraw from the business.

But in recent months ferry companies that serve Britain, including DFDS and P&O Ferries, have also stopped carrying laboratory animals.

Michelle Ulyatt, a spokeswoman for P&O Ferries, said its decision to halt live animal imports was taken last year under sustained pressure from anti-vivisection groups.

Our primary concern is ensuring staff safety and our corporate reputation, she told Reuters, adding that at the height of campaigns against ferry companies, letter bombs had been sent to transport executives.

Michelle Thew of the British Union for the Abolition of Vivisection said airlines and ferry companies were responding to the widespread public concern about using animals for research. Animal rights campaigners believe it is morally indefensible to inflict pain and suffering on animals when it is not for their benefit, she said.

DILEMMA FOR CAMERON

Rodents like mice, rats and guinea pigs represent the majority - around 82 percent - of animals used in research, so more of these animals are transported. According to government data from 2010, just 0.7 percent of all experiments performed in the UK used animals transported from other countries.

The stand-off over importing animals for research poses a dilemma for Prime Minister David Cameron, who has said he is determined to make Britain a prime location for scientific investment, particularly in the pharmaceutical sector.

We're going to be more flexible, more competitive, more hungry for your business than ever before, he told executives at a recent global pharma and biotech conference in London.

Britain has been particularly reliant on pharmaceutical firms for success in manufacturing and is home to two of the world's top drug companies in GlaxoSmithKline and AstraZeneca. But the industry has been under pressure in recent years and forced to make cuts.

Cameron has said Britain is feeling the fall-out of the global challenges now facing the sector, with the world's No. 1 pharma firm Pfizer closing a research and development site in Sandwich, southern England, and AstraZeneca pulling out of its Charnwood research site in central England.

Colin Blakemore, professor of Neuroscience at Oxford University, said the public need to be made aware that vital research - on brain disease, cancer and heart disease - is already being impeded because of the targeting of airlines and ferry companies by tiny, unrepresentative pressure groups.

It's important not to give in to intimidation. The government and the medical research community must support the transport companies and explain to the public why the importation of small numbers of animals... is crucial for medical progress, he said in an emailed comment.

Science minister David Willetts said this was a serious problem which the government was determined to tackle.

We are trying to hammer out a deal in which both the life sciences industry agree a kind of code of conduct on exactly how animals... will be transported, and in return the transport industry... would all agree that they would continue to transport animals, he told BBC radio.

That's what we still hope we can put together. It makes sense for everyone.

(Editing by Greg Mahlich and Mike Nesbit)