Blue chip shares surged in afternoon trading after the cost of living in the UK unexpectedly shrank last month, according to official figures.

The consumer prices index measure of inflation slipped to 0.9% in the year to October, the Office for National Statistics said, down from the 1.0% rise the previous month and short of expectations that it would hit 1.1%.

The FTSE 100 Index rose 42.4 points to 6795.6, as sterling fell 0.64% against the dollar, fetching $1.2405, and making top flight stocks a cheaper buy for international investors. The FTSE 250 Index lifted 72.1 points to 17544.5.

IG chief market analyst Chris Beauchamp said: "An unexpected drop in UK prices has sent the pound into freefall again versus the dollar, which has meant that the FTSE 100 is enjoying the benefits of a weaker currency."

Budget carrier EasyJet said its pre-tax profits fell 27.9% to £495m ($618m) in the year to the end of September, blaming the weak pound, terror attacks, and air traffic control strikes.

But analysts at Numis said: "In a very difficult year the return on capital employed continued to be very acceptable at 14.6%." Shares in the airline were more than 5% higher, or 57p to 1089p.

In afternoon trading, the biggest risers in the FTSE 100 Index were Hikma Pharmaceuticals (+128p to 1752p), EasyJet (+57p to 1089p), Tesco (+10.7p to 216.6p), Morrisons (+10.2p to 222.8p) and BP (+12.7p to 446.3p).

The biggest fallers in the FTSE 100 Index were Anglo American (-76p to 1099p), Antofagasta (-40p to 666p), Glencore (-14.9p to 268p), BHP Billiton (-64p to 1272.5p) and Rio Tinto (-135.5p to 3010p).

In afternoon trading, the biggest risers in the FTSE 250 Index were Polypipe Group (+20p to 280p), Amec Foster Wheeler (+31.3p to 451.3p), Tullow Oil (+17p to 256.2p), Laird (+7.6p to 140.6p) and Intermediate Capital (+33p to 666.5p).

The biggest fallers in the FTSE 250 Index were Kaz Minerals (-30.7p to 333.6p), Vedanta Resources (-40p to 774p), BTG (-31.5p to 614.5p), TalkTalk Telecom (-9.2p to 192p) and JRP Group (-4.6p to 125.4p).