"On average it is 157 days longer for Switzerland and on average it takes Canada 140 days longer.

"It takes longer, it is more complicated and it adds an uncertainty to the whole process which is uncertain enough as it is."

“We are clear that we want to stay in because we believe that the disruption is significant,” he said.

The scientists said that there was a risk that if Britain left the EU, it would have to re-register 130 products.

The MHRA chief said he did not know how the watchdog would cope with the burden of work if it was not able to share its workload with other EU countries.

Sir Mike said the body would lose “a very substantial proportion” of its income if it could only authorise products for a British market, instead of granting approval across Europe.

Professor Bruce Campbell, non-executive director at the MHRA, said a worst-case scenario could mean that it is harder to spot when things go wrong with medical devices.

He said: "There are around half a million medical devices out there and they all need some kind of regulation.

"Some need complex licensing and complex regulation and all of this is done through a carefully constructed and collaborative European system of licensing and surveillance."