LONDON (Reuters) - British car production rose by 26 percent year on year in May thanks to particularly strong demand for exports, but momentum could be halted by a loss of tariff-free access to Europe, an industry body said on Thursday.

The country's overwhelmingly foreign-owned car industry was at the forefront of big business's unsuccessful efforts to persuade Britons to vote to stay in the European Union and is now seeking guarantees that uninhibited access to its biggest market will continue.

In May British plants built 150,802 vehicles, the Society of Motor Manufacturers and Traders (SMMT) said on Thursday, helping to push up year-to-date production by nearly 14 percent in the first five months of the year.

"For this success to continue, we need government to maintain economic stability and help deliver the wider benefits -- including free access to our biggest market -- which have helped make the sector so globally competitive," said SMMT Chief Executive Mike Hawes.

(Reporting by Costas Pitas; Editing by David Goodman)