LONDON (Reuters) - Thousands of HSBC customers in Britain on Friday reported they were unable to access some mobile and online banking services, the latest in a long-running series of such problems for British banks.

Website Downdetector which tracks service outages reported complaints began shortly after 0700 GMT and peaked at more than 4,000 by 0900, and HSBC acknowledged the problems.

"We’re working hard to restore Mobile and Online Banking service, and the authorising of online card purchases via the app," the bank said.

Consumer advocates said the problems at Britain's biggest bank would be especially acute given it is one of the country's most active shopping days.

"This HSBC outage will cause a real headache for a lot of its customers. In the worst cases it could prevent people making essential payments such as rent and bills, but it also falls on Black Friday, one of the busiest shopping days of the year," said Sam Richardson, deputy editor of consumer advocacy magazine Which?.

Regulators and politicians in recent years have repeatedly called on banks to prevent such problems, at a time when lenders are reducing their physical presence and encouraging customers to rely on digital services.

The Bank of England in April last year told banks to speed up recovery from outages in order to avoid undermining public confidence in the financial sector.