The former economics teacher said three in 10 pupils got good GCSEs in 1997 but claimed that was 60 per cent. It was an attempt to attack Education Secretary Michael Gove's ability at maths, but it backfired and prompted the cabinet minister to say percentages were not Labour's strong point.
Following reports that the Government was considering ditching GCSEs in favour of a return to O-level style examinations, Mr Brennan said: ''Standards rose under Labour because we focused on literacy and numeracy.''
The Oxford graduate and former head of economics at Radyr Comprehensive School in Cardiff added: ''It was we who inherited a weak system on maths and English from the Tories.
''Only three in 10 pupils, that's 60 per cent because I know the Secretary of State is not very good at maths, only three in 10 pupils got a good GCSE in 1997.''
Commons Speaker John Bercow was forced to intervene to appeal for calm as Tory MPs heckled the Labour frontbencher, who was standing in for Stephen Twigg, the shadow education secretary.
Mr Brennan said: ''I was just testing their numeracy, it is of course 30.''
While Mr Gove was speaking, Labour MPs questioned his use of statistics but he shot back: ''I think, given the questions that were put by the Honourable Member, trading percentages across the despatch box is not an area in which Labour can consider themselves to be strong.'