Barclays executives could face charges next month over secret payments the bank made to Qatari investors, Reuters news agency cited unidentified sources as saying on Friday.Former chief executives Bob Diamond and John Varley, former finance director Chris Lucas and former tax advisory boss Roger Jenkins have all been interviewed during a two-year investigation by the Serious Fraud Office (SFO).The SFO could decide as soon as September whether to charge the bank's former executives, even though it did not specify why the payments Barclays made to Qatar Holdings were being investigated, Reuters said."We are making progress with this case and we are not going away," Reuters reported SFO chief David Green as saying.Barclays and Diamond declined to comment and the other parties involved could not be reached for comment, Reuters reported.Varley was the bank's chief executive when Barclays received cash injections from Qatar, while Diamond was in charge of the investment bank division and replaced Varley in 2010.Diamond resigned in 2012 after Barclays was fined for rigging Libor interest rates.Were Barclays executives to be charged, they would become the most senior figures prosecuted in the wake of the 2007-08 financial meltdown, which hit the world's financial system.While Royal Bank of Scotland and rival Lloyds had to be bailed out by the government during the crisis, thus suffering various kinds of restrictions, Barclays managed to stay afloat thanks to two emergency cash injections, worth almost £12bn, from Middle East investors.The bank admitted paying £116m in advisory fees and commissions to Qatar Holdings but it failed to reveal another payment, worth £322m, in two "advisory services agreements" with the Qatari group, Britain's Financial Conduct Authority (FCA) said.The FCA fined Barclays £50m for the non-disclosure, saying the bank's behaviour could have broken its duty to act with integrity to all its shareholders.The FCA's findings are being contested by Barclays, as the bank claims it disclosed one of the agreements without revealing the amount involved.At the time when the deal was struck, Barclays' shareholders made their disapproval public, incensed by the fact the Qatari wealth fund was offered better terms than existing investors, thanks to which the Gulf state secured healthy profits.The Qatari wealth fund remains one of Barclays' three biggest shareholders, with a 5% share in the group.Barclays shares were up 0.07% to 218.15p at 16:24 on Friday.DC