The FTSE 100 fell 0.85% or 46.36 points to 5,392.83 this morning with Barclays among the biggest losers.
The FTSE 100 opened higher, up 0.47% or 25.67 points to 5,453.82, in response to Friday's better than expected US jobs data.
Britain's leading share index has fallen back into the red after enjoying modest gains in early Thursday trading.
Prudential's 1.5% rise in early trading, following better than expected first-half profits, helped the FTSE edge 0.3% higher to 5257.79 points.
The FTSE 100 opened strongly at the start of the week, boosted by Friday's late rally on Wall Street and positive corporate news.
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.