* Drugs watchdog to relocate to EU country after Brexit
* European Medicines Agency braced for staff losses
* Drugs for cancer, other diseases may be delayed -EMA head
* In worst-case scenario agency would not function
LONDON, Oct 3 (Reuters) - Access to new medicines and safety checks on existing treatments will be jeopardised if politicians pick a new home for Europe's London-based drugs regulator that is unacceptable to staff, its executive director told Reuters.
Cancer drugs and therapies for rare diseases could be particularly affected by an exodus of key scientific and administrative staff during the move, which has been triggered by Britain's decision to leave the European Union. The European Medicines Agency (EMA) must be headquartered in an EU country.
"Oncology is a good example. The pipelines are very promising for new cancer options and if there is severe disruption those might be delayed or prove impossible to approve," said EMA chief Guido Rasi.
Based in London since 1995, with a staff of around 890, the EMA acts as a one-stop-shop for approving and monitoring the safety of drugs across Europe.
Now it is about to be uprooted as a result of Brexit and a staff survey last week found that between 19 percent and 94 percent of employees were likely to leave after the move, depending on which of 19 possible locations is chosen.
At stake is not only the smooth-running of the European Union's drug approval process - vital for both patients and companies - but also public safety, if regulators fail to react to a side-effect problem or quality issue in a timely fashion, Rasi said.
The EMA deals with more than a million reports of adverse drug reactions every year. It also inspects manufacturers worldwide and in recent years has suspended hundreds of drugs that fall short of testing standards.
Most recently, the agency's safety role was highlighted when it held a high-profile hearing on links between Sanofi's epilepsy drug valproate and birth defects.
"Europe now is called on to decide not where to relocate an agency but how to protect an activity that is crucial for public health," Rasi said in an interview.
NO BACK-UP PLAN
Because the work of regulating medicines is delegated by EU member states to the EMA, there is no back-up plan if the agency is relocated from 2019 in a city where it is impossible to operate effectively due to staff losses.
Rasi said that in a worst-case scenario, the agency would simply no longer be able to function. Drug approvals would grind to a halt and Europe might have to import medicines - something that would require new legislation.
Picking Amsterdam, Barcelona, Vienna, Milan or Copenhagen as the new headquarters would be the best option for retaining staff, according to the survey of its workers. Any of the other 14 sites would spark large staff losses.
All of the top five candidate cities favoured by EMA staff are in countries that already host one or more EU agencies. Some of the lower ranking cities are in Bulgaria, Croatia, Slovakia and Romania, where there are none.
Rasi said the scale of the potential staff exodus was "much worse than anticipated" but reflected the upheaval facing employees, many of whom have children established in London schools and working spouses in the city.
"This has not been reflected upon enough," he said.
The European Commission on Saturday published its assessment of different locations for the EMA and the smaller European Banking Authority, which will also have to leave London because of Brexit.
The Commission did not rank the rival bidding cities, many of which have lined up sweetheart deals to lure the two agencies.
EU leaders will make the final location decision on Nov. 20, but the need to ensure business continuity could clash with another cherished ambition of spreading the bloc's agencies more evenly across Europe, particularly in eastern member states.
Relocating the EMA before Britain leaves the EU in March 2019, as current plans dictate, involves a very tight schedule. In 2014, the agency moved just 800 metres to a new office block within London's Canary Wharf financial district - a shift that took three years from signing a lease to moving in.
Rasi, at least, is committed to go wherever his political masters send him. "The captain is the last to abandon the ship," he said. (Reporting by Ben Hirschler, editing by Peter Millership)