Metropolitan Police sources confirmed that units had been despatched to the Millbank offices following a series of calls from senior activists and MPs, with the most recent call to 999 made by Tory Leader David Cameron.
A Scotland Yard spokesman said, "we were called to an address in Millbank, SW1, following complaints of antisocial behaviour and noise pollution.
"We discovered an overweight lady singing outside the building, and we understand that she has been doing so since 10pm last night despite hopes that she would have finished singing by early morning."
Sources said that one arrest has been made, but that as far as the Conservative Party were concerned, it was unlikely the fat lady would cease singing for some time yet.
Reports that David Cameron has no cigar remain unconfirmed.