* Industry fears disruption at European Medicines Agency
* Shifting home after a 'Brexit' could slow drug approvals
* Loss of British scientific expertise would be major blow
* Brexit may also cast uncertainty on UK-based EU bank authority
By Ben Hirschler
LONDON, Jan 29 (Reuters) - Fears of a British exit from the European Union are growing in a corner of London's Canary Wharf financial district - but this time it is pharmaceutical executives rather than bankers who are worried.
A so-called Brexit would threaten the future of the London-based European Medicines Agency (EMA), which approves medicines for all EU countries, potentially disrupting healthcare regulation in the world's biggest trading bloc.
With a full-time staff of more than 600, the EMA is the largest EU body in Britain - which is also home to the European Banking Authority - and has overseen pan-European drug approvals since 1995 from its headquarters tucked away among global banks.
Before that, Europe relied on a fragmented system of national regulation that was cumbersome for companies seeking to reach Europe's population of half a billion potential patients.
In the event of a Brexit, which could also cast uncertainty over the future of the bank authority, Europe's equivalent of the U.S. Food and Drug Administration may have to find a new home, in a jolt to the current drug approval system.
This could slow the approvals of medicines across Europe during this transition process, including in Britain if it has to re-engineer its system.
Losing Britain could also punch a big hole in the EMA's scientific capability, since British experts are the biggest single contributors to its drug assessment system.
Opinion polls suggest UK voters are split almost 50-50 on whether to pull Britain out of the EU in a referendum which Prime Minister David Cameron is likely to schedule for later this year.
"The uncertainty this creates is not good for the industry," Richard Bergstrom, director general of the European Federation of Pharmaceutical Industries and Associations, told Reuters.
Exactly what would happen if Britons vote "out" is unclear, since EU chief executive Jean-Claude Juncker has ordered officials not to discuss or study the impact of Brexit.
But many industry officials believe the EMA, as an EU agency governed by EU legislation, would relocate from London to a remaining member state.
Bergstrom said the process would at best be "messy" and could be "very disruptive", depending on transition arrangements.
The loss of British expertise would also be a major blow to the agency; in 2014, the latest year for which figures are available, British experts were leaders or co-leaders in examining 27 new drug applications submitted to the EMA, according to the agency's annual report.
That compares with 15 for Germany, 14 each for Spain and the Netherlands, and 13 for Sweden, the next most active countries.
It is possible Britain could continue to participate in the EMA system as a non-EU member, as happens with Norway, Iceland and Liechtenstein, but this would be subject to negotiation.
EMA officials said the agency would not speculate on the result of the British referendum or its potential consequences.
European Commission spokeswoman Mina Andreeva said the EU's executive arm would not answer "hypothetical questions", adding "there is no other plan" than to find a deal to keep Britain in the bloc.
There is also concern that the life sciences division of Europe's new Unified Patent Court might have to move from London before it even opens - a lesser but still important setback.
The court is designed to simplify patent litigation by limiting disputes to a single forum and a lease for the London branch was signed in August, ahead of a potential 2016 opening.
Industry bodies representing British-based pharmaceutical and biotechnology companies have expressed concern about the Brexit threat in submissions to an ongoing House of Lords inquiry.
The issue may not be top of the agenda for Cameron but any damage to the sector would be embarrassing, since he has championed pharma as a rare industrial bright spot for Britain, led by global players like GlaxoSmithKline and AstraZeneca.
While the British medicines market, accounting for just 3 percent of global sales, may be small, the country is an important base for multinationals.
"The UK is a very logical and attractive headquarters location for life sciences companies entering Europe and I would hate to see that imperilled," said Richard Barker, founding director of the Centre for the Advancement of Sustainable Medical Innovation, a partnership between Oxford University and University College London.
The only other EU agency based in Britain is the European Banking Authority (EBA), established in 2011 and responsible for bank stress tests.
The EBA moved to its new home in Canary Wharf in December 2014, so its lease would have been agreed when a referendum on Britain's EU membership was already a possibility. The EBA declined to comment on whether its lease had a specific Brexit break clause. (Additional reporting by Huw Jones; Editing by Pravin Char)