Barclays shares are 3% lower in early trading despite posting profits of almost £4bn in the first half.
The FTSE fell in early trading in reaction to losses on Wall Street overnight and a weak opening in European markets.
London's top stocks have given up some of yesterday's triple-digit gains in early trading, with the FTSE 100 down 0.72%.
The FTSE 100 has soared 1.98% this morning as HSBC more than doubled pre-tax profit to £7bn.
The FTSE was down in early trading at 5311.91, representing a drop of 2.04 points (0.04%), ahead of US GDP data.
The FTSE edged slightly higher this morning, buoyed by upbeat earnings announcements from AstraZeneca and BAE Systems.
Banks are once again leading the FTSE 100 gains in early trading, after a number of stocks soared upwards of 10% yesterday on the relaxing of Basel III rules.
Banks pushed the FTSE higher by 0.55% to 5380.35 on news the Basel Committee proposed to water down its capital and liquidity reform package.
UPDATE 12pm: The FTSE 100 index has climbed almost 1.6% in morning trading after strong late gains overnight on Wall Street.
Asian markets were in decline today following the sharp 3% fall for US indices on Friday.