“The Daily Telegraph can disclose that the “raw” results of YouGov surveys in the month up to mid-March, covering more than 16,000 people, indicated that the Conservatives had a lead of more than 12 per cent. However, the figures – leaked to The Daily Telegraph – were then “weighted” using an undisclosed YouGov formula which reduced the lead to six per cent…. In recent weeks, YouGov and Experian, one of the country’s biggest market research firms, co-operated to compile a major study on the voting intentions of more than 16,000 people. Experian concluded that, overall, the Conservative lead over Labour was 12.5 percentage points, with the Tories on 40.8 per cent, Labour on 28.3 per cent and the Liberal Democrats on 17.4 per cent. After “re-weighting” by Mr Kellner, the Tory lead fell to six per cent. ”

YouGov pollster “gives Labour an unfair advantage”