London’s top flight index ended the month on a positive note after shrugging off worse-than-expected US growth figures and big losses at taxpayer-backed Royal Bank of Scotland.

The FTSE 100 closed up 34.9 points at 6360.8, despite a 7% fall in shares at part-nationalised Royal Bank of Scotland, after it revealed its fifth year of losses since being bailed out by the taxpayer.

Blue chips were also unmoved by the flat opening on Wall Street’s Dow Jones Industrial Average after US GDP data posted its worst performance in nearly two years.

The growth figures showed that while the US economy grew 0.1% between October and December in a reversal of the initial 0.1% contraction reported last month, the revision was well below the 0.5% growth expected by economists.

It was central bank bosses who provided a boost to trader sentiment after offering vigorous defences of their monetary easing policies.

Federal Reserve chairman Ben Bernanke talked up the bank’s asset purchases programme in front of US politicians, while there were similar reassuring comments from European Central Bank head Mario Draghi.

Mr Draghi’s dovish tone, which fuelled fears of an interest rate cut, provided a welcome boost to the struggling pound, which was up against the euro at 1.16. It was also up against the US dollar at 1.52.

The biggest FTSE 100 risers were International Airlines Group up 17.5p to 239.2p, ITV ahead 5.2p to 124.2p, GKN 8.8p higher at 273p and Standard Life up 10.6p to 352.5p.

The biggest FTSE 100 fallers were Kazakhmys down 58p to 619p, Royal Bank of Scotland off 22.9p to 323.9p, Capita 24.5p lower at 823.5p and Petrofac down 43p to 1454p.