FILE PHOTO: A Swiss International aircraft flies past the HSBC headquarters building in the Canary Wharf financial district in east London February 15, 2015. REUTERS/Peter Nicholls/File Photo

LONDON (Reuters) - HSBC UK HSBA.L said on Tuesday some of its customers were struggling to access online banking, the second outage of the lender's digital services in weeks.

“We are investigating further and will provide further updates,” the bank said on Twitter after a number of customers used the social media platform to flag problems accessing HSBC’s site.

The bank’s mobile banking app also suffered a brief glitch in September, one of a series of outages at Britain’s biggest lenders in the past few months. [nL8N1WE3E0]

Technical problems at banks have prompted criticism from customers and from lawmakers, who in September called on Royal Bank of Scotland RBS.L and Barclays BARC.L to explain what caused the problems and how they would compensate affected customers. [nL3N1W730L]

Outages can cause significant disruption to customers, who are increasingly reliant on digital services as banks close branches and encourage clients to move online.

The impact of a severe outage was brought into sharp focus earlier this year, when mid-sized lender TSB was plunged into chaos after a botched IT migration saw some customers locked out of their accounts for over a week.

The outage tarnished TSB’s brand just as it was gearing up to try and win more market share from Britain’s biggest banks, cost hundreds of millions of pounds and prompted the resignation of the bank’s CEO Paul Pester. [nL8N1VQ1N9]