Former Labour MP Margaret Moran claimed nearly her entire annual allowance in one bogus expense entry, a jury has heard.
The 57-year-old submitted an invoice for £22,500 in August 2008 - just under the annual maximum expense allowance for an MP - to treat dry rot at her Southampton home, using the money instead to fund "home improvements", the court heard.
Moran, who served as MP for Luton South from 1997 until the 2010 general election, is accused of falsely claiming around £60,000 in parliamentary expenses between 2004 and 2008.
Southwark Crown Court in London heard she was able to make the dry rot claim by "flipping" her two homes - changing which property was her second home and therefore allowing her to claim expenses on it. She also allegedly changed dates on invoices for the work so that the money would be paid.
Prosecutor Peter Wright QC said: "In reality, she secured the cost of extensive home improvements, at an address in Southampton that was not then her second home, at public expense."
Moran is accused of falsely claiming thousands of pounds by submitting fake invoices.
One in August 2007 was for £14,805 - apparently for boiler repairs and work on her conservatory in her constituency home in Luton, when it was actually at her house in Southampton. On another fake bill for more than £4,000, address details given for a building firm were those of an elderly couple.
She also claimed more than £2,000 for a landline at her flat when there was no phone line fitted, the jury heard, and for carpet for three bedrooms for her one-bedroom Westminster flat. Mr Wright said: "It was rather a lot of carpet for a one-bedroom flat in London."
Moran, of Ivy Road, St Denys, Southampton, is accused of 15 charges of false accounting and six of using a false instrument over the claims for parliamentary expenses.
The former politician was found unfit to stand trial due to mental health issues, so proceedings are taking place in her absence. Rather than finding her guilty, jurors have to decide whether Moran did commit the acts alleged in the charges, and whether they amount to the offences with which she is charged.