(Reuters) - Hiring levels in London investment banking have picked up in recent weeks, though it is too early to say whether this will continue in the wake of Britain's vote to leave the European Union, recruitment firm Robert Walters (>> Robert Walters PLC) said on Monday.

There have been concerns that banks in Britain will shift some jobs abroad if the Brexit vote leads them to lose the ability to offer services across the European Union - or so called passporting rights - from a base in London.

Top bankers warned last week they could start moving staff abroad as early as next year.

Robert Walters, chief executive of the company that shares his name, told Reuters there had been a pick up in hiring at London investment banks towards the end of the company's third quarter to Sept. 30, mainly for risk and compliance roles.

But he cautioned recruitment in banking tended to be volatile, with companies often announcing new jobs only to come out with "draconian hiring freezes" just weeks later.

"Banking is an impossible one to predict at the best of times, and overlay on that Brexit and passporting issues and it makes it even more difficult to predict," he said.

Larger rival PageGroup (>> Pagegroup PLC) said last week that confidence among employers in Britain was "fragile" following the Brexit vote, with multinational financial services firms particularly holding off from hiring. UK recruiter Hays (>> Hays plc) is expected to post quarterly results on Tuesday.

Robert Walters, which also places workers in engineering, legal and marketing jobs, said London hiring had generally picked up in September, after a fall off ahead of and after the June 23 referendum.

The company said UK gross profit rose 9 percent to 23.4 million pounds in the quarter, on growth in its outsourcing business as well as trade finance jobs and some regions outside London.

It had reported comparable growth of 4 percent for the first six months of 2016.

At 1025 GMT, its shares were up 2.3 percent at 349.75 pence.

($1 = 0.8042 pounds)

(Reporting by Esha Vaish in Bengaluru; Editing by Louise Heavens and Mark Potter)

By Esha Vaish

Stocks treated in this article : Robert Walters PLC, Hays plc, Pagegroup PLC