Britain's anti-fraud agency has asked former Barclays executives to give evidence as part of an investigation into undisclosed payments the bank made to Qatari investors in 2008, the Financial Times reported, citing sources.

The FT said the Serious Fraud Office had served Section 2 notices on directors who were on the Barclays board when it secured almost £12 billion pounds ($19.61 billion), mostly from Middle East investors, to avoid a state bailout during the 2008 credit crisis.

Section 2 notices deny those giving evidence a right to silence and require recipients to hand over documents to the SFO - in exchange, the recipients will not be prosecuted provided they do not lie.

The two-year investigation has so far been fraught with disputes over accessing key evidence, the FT cited people familiar with the investigation as saying.

The SFO declined to comment and Barclays could not be reached outside of regular business hours.

The bank revealed previously that it had paid out £116 million in advisory fees and commission to Qatar Holdings as part of the 2008 deal with investors. However, Britain's Financial Conduct Authority (FCA) said the bank had failed to reveal another £322 million in two "advisory services agreements" with the Qatari company.

Barclays has been contesting the FCA findings and the FCA case is on hold pending the outcome of the SFO investigation. - Reuters