British drug companies have been struggling to attract top talent from overseas since the Brexit vote, research has ­revealed.

The proportion of applicants from outside the UK for senior roles at pharmaceutical firms has fallen sharply from around 40pc to 15pc in the year and a half since the referendum, data from recruiter DHR International shared exclusively with The Telegraph has shown.

The firm, which specialises in filling executive positions, says it is already starting to find problems filling senior vacancies.

Large British drug firms said DHR’s findings chimed with their experience. One insider said overseas candidates were “turning us down for roles because of the uncertainty around Brexit” and it remained a big concern among existing staff who had joined from abroad.

Drug maker AstraZeneca said that, while it was “in part reassured” by the Government’s commitment to the sector since the referendum, it remained concerned.