Lawyers for the Conservative party have written to the Electoral Commission questioning the impartiality of one of the organisation's most senior staff, the Telegraph understands.

Louise Edwards, the commission's head of compliance, reportedly posted negative comments about the party online in which she said she couldn't "understand what people were thinking" after electing David Cameron.

It came as a second Conservative letter accused the commission of bias for not investigating Labour, the SNP and the Liberal Democrats over reports they did not properly declare election spending during the 2015 campaign.