The London market struggled for direction despite data showing that the UK's manufacturing sector rebounded sharply in August.
The Markit/CIPS purchasing managers' index (PMI) for the sector jumped to 53.3 last month from 48.3 in July. A figure above 50 indicates growth.
The FTSE 100 Index slipped 6.4 points to 6775.2, even though the PMI survey was the largest month-on-month increase in its 25-year history. The FTSE 250 Index, a closer reflection of UK firms, lifted 190.4 points to 17923.2.
Spreadex financial analyst Connor Campbell said: "In one of those instances of contradictory market nonsense the surprise manufacturing PMI sent the pound sharply higher – to the tune of 1% – against both the dollar and the euro despite the fact that the survey underwent such an increase thanks to sterling's sustained weakness across August causing a swell in cheaper exports."
In afternoon trading the biggest risers on the FTSE 100 Index were Berkeley Group (+123p to 2795p), Taylor Wimpey (+6.4p to 167.7p), Lloyds Banking (+2.2p to 61.6p), Persimmon (+63p to 1887p) and 3i Group (+18.5p to 633p).
The biggest fallers on the FTSE 100 Index were Hikma Pharmaceuticals (-52p to 2088p), BHP Billiton (-21.2p to 968.7p), Royal Dutch Shell (-37p to 1905p), Fresnillo (-29p to 1577p) and GlaxoSmithKline (-29p to 1610p).
In afternoon trading the biggest risers on the FTSE 250 Index were Allied Minds (+33.7p to 358.5p), Sports Direct International (+22.5p to 319.8p), Thomas Cook (+3.4p to 73p), IP Group (+8.7p to 198.7p) and Bovis Homes (+40p to 936p).
The biggest fallers on the FTSE 250 Index were Ascential (-10.9p to 254.1p), Centamin (-4.7p to 143.8p), Stagecoach (-5.1p to 222.5p), Aggreko (-19p to 1000p) and Acacia Mining (-8.2p to 452.5p).