Traces of cocaine have been found in toilet cubicles throughout the Houses of Parliament in tests carried out by a tabloid newspaper.
Journalists from the Sun found cocaine at nine locations after carrying out police-style swab tests on facilities inside the Palace of Westminster.
The drug was found in private areas of the building, as well as in areas to which both staff and the public have access, the newspaper reported.
"The findings suggest the drug is regularly being snorted at both the Commons and the Lords - with users defying airport-style security checks and a 500-strong team of cops and security officers," the Sun reported.
The tabloid said it carried out forensic tests after receiving a tip-off from a parliamentary insider. The newspaper has since handed its findings to "officials", it said.
"Acting on a tip-off from a Commons whistleblower, we started by testing toilets outside Strangers' Bar, a favourite haunt of MPs. Our team found traces of cocaine in three ladies' cubicles and a gents'," the newspaper revealed.
"We then searched toilets on the wood-panelled House of Lords committee corridor - and on one toilet seat, a swab turned bright blue. It stained traces on the seat, revealing a 'line' of coke.
"There were also scars indicating chopping of the drug had taken place. Our undercover team wiped cocaine indicator swabs against toilet seats, loo roll holders and hand dryers in dozens of locations.
"All of Parliament's toilets are cleaned on a regular basis, suggesting the white powder had been snorted in the past few hours.
"More traces were found in private areas close to leading Tory and LibDem MPs' offices in Portcullis House - but there is no suggestion any MPs have been involved."
Tory MP Douglas Carswell said the findings revealed "something rotten" in the state of British politics. "With decadence comes something rotten. It suggests there is something rotten about the institution itself," he said.
Prime Minister David Cameron, once a member of Oxford University's Bullingdon Club, has famously refused to deny he ever used cocaine in his student days.
Parliament's pay watchdog last week recommended MPs be awarded a pay rise of £7,500, or 11%, bringing their total pay to £74,000 a year. At 2010 UK street prices, that equates to 188 grammes of cocaine.
Robert Oxley of the TaxPayers' Alliance said: "It's worrying. Pay is high enough in Westminster without the occupants being high too."