The Conservative Party has made a formal complaint to the BBC about its coverage of the local elections in May.
The Conservatives say the BBC played down Tory success
The party says the broadcaster played down its success and consistently over-estimated the Liberal Democrats' share of the vote.
The Tories have handed over a dossier setting out their complaints to the BBC.
They allege that the BBC "followed a pre-conceived agenda" that the election results "were going to leave the Conservative Party in crisis".
They say that the BBC "failed accurately to report or predict Conservative gains, put more emphasis on opinion polls than actual results, and spent too little time highlighting the issues on which people were voting".
A BBC spokeswoman said: "We will investigate fully. We do take all complaints seriously."
The election saw the Tories take more than 560 seats - gains described by party leader Iain Duncan Smith as "very heartening".
He said the local election success would be a springboard to restoring them as a real threat to government.
Mrs May said the BBC's coverage gave viewers "the impression that the Conservative party was in crisis, that the party had not done very well in the elections and that many Conservatives supported Crispin Blunt's personal attack on Iain Duncan Smith".
Mr Blunt had quit his frontbench post as polls closed.
Mrs May said: "All these impressions are demonstrably untrue and, anyway, should not have played such a prominent role in a programme entitled 'Vote 2003'.
"The agenda, script and questioning appeared to have been set in advance on the theme of 'Conservatives in crisis'."
She said the "real story" of the election was Tory gains, a boost to Mr Duncan Smith's leadership, a fall in Labour support and "small" Liberal Democrat gains.
But the Tory chairman said this had only been "reluctantly accepted over the next 24 hours across the BBC's output".