Lady Sylvia Hermon says she only recently discovered the mistake
North Down Ulster Unionist MP Lady Sylvia Hermon has repaid £2,730 in expenses for rent on a London flat.
Lady Hermon said she was overpaid by two months rental allowance office during 2005-2006.
She said she only discovered the error when she contacted the Fees Office on Monday.
"Even though I immediately reimbursed the House of Commons with the £2,730, I remain profoundly upset and embarrassed," she said.
She said that she had written on the claim forms that she wanted them to be checked by the office.
She told the BBC she had "naively assumed" that the Fees Office would have checked so was relaxed amid the furore over MPs expenses.
But when she phoned the office she said she was shocked to learn that there had been an error.
She also complained that the Fees Office had failed to apologise to her.
Lady Sylvia was elected in 2001 and rented a flat 20-minutes from the House of Commons. Three years later she moved to a one-bedroom property which was closer to the Commons.
I didn't claim for dog food, chandeliers or any other weird and exotic items
Lady Sylivia Hermon
She ended the tenancy early in 2008, after her husband, former RUC Chief Constable Sir Jack Hermon, was admitted to Downshire Hospital. Sir Jack had Alzheimer's disease and died in November that year.
She said since then she had used hotels in London when she had to stay over in London.
"I've never bought property nor had a mortgage in London; I didn't have a television at any stage, didn't watch DVDs of any nature, didn't claim for food in London, furnishings, security or cleaning, didn't claim for dog food, chandeliers or for any other weird and exotic items," she said.
She said that during 2005, when the claim was made, she had been coping with her husbands deteriorating health in the aftermath of an election campaign.
"The pressure on me was enormous at that time, pre-devolution, when every piece of Northern Ireland legislation had to go through the House of Commons and I was the only Ulster Unionist voice," she said.
"There can, however, be no excuses. The mistakes were mine, which I have rectified and for which I am extremely sorry."
She said that she had been told by the Fees Office that given the pressure she was under they were "surprised" there were not more mistakes.
She also expressed outrage that the Fees Office had paid other MPs for food, swimming pools and chandeliers when she was unable to claim for a Heathrow Express ticket to get to her place of work.
"So when I learned other MPs have claimed for bags of manure and been paid for them and paid for swimming pools, I am furious," she said.
Asked about the claims of some Conservative MPs with whom her party is now affiliated for electoral purposes, Lady Hermon said claims for some items were "indefensible, immoral, cringe-making and outrageous."
BBC Northern Ireland political reporter Stephen Walker asked other Northern Ireland MPs if they had expenses voters might question.
He said that South Down SDLP MP Eddie McGrady - did not want to talk about expenses at all, but that his party leader Mark Durkan went further.
The Foyle MP said all the claims he has made were legitimate but he accepted there was a concern amongst the public about the expenses system.
"In this current environment where anything can be questioned," he said.
"It could be the case that myself and others err on the side of caution and propriety and end up paying some money back."
Upper Bann DUP MP David Simpson said everything he claimed for was for the "good of the constituency" and when asked if he thought he may have to pay anything back replied: "Absolutely not."
Lagan Valley DUP MP Jeffrey Donaldson said that there was "nothing he was aware of" that could be questioned in his expenses he said that he had "only just received the receipts".
The South Antrim DUP MP Willie McCrea said he hadn't had the opportunity to go through all his claims.
He said he was satisfied his expenses and allowances fell within the guidelines. However he said 'if there is anything that is not correct I have no problems in making amends but I have to see all my claims first' .
The Daily Telegraph has been outlining the expenses claimed by MPs for the last week.
While it has mostly concerned itself with the front bench of the major parties and some Sinn Fein claims, Stephen Walker said there could be more attention paid to local MPs by the paper later this week.
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