All four MPs were the subject of Daily Telegraph reports
Prime Minister Gordon Brown has vowed to take "all the action that is necessary" to discipline Labour MPs who have "misbehaved" over expenses.
A Labour panel has met for the first time to discuss whether MPs under fire over expenses can seek re-election.
It will decide if Margaret Moran, Elliot Morley, Ian Gibson and David Chaytor can stand again for Labour.
It came as Tory leader David Cameron ordered his MPs to talk to their constituents about their expenses.
Mr Brown insisted he was taking a "strong line" against alleged offenders and his aim was to "make sure that politics is something that is about service to the community and never about people serving themselves".
He said any MPs found to have "misbehaved" by the three-member disciplinary panel, set up by Labour's ruling National Executive Committee, "will be told they can not stand at the next election".
The relationship between voters and politicians has changed forever because of these allegations
Justice Secretary Jack Straw
The so-called "star chamber", which met for the first time on Wednesday, said in a statement it was "gathering evidence from all parties concerned" and the party would "make a further announcement when it has come to its conclusions".
It added: "All members of the panel agreed on the need for rapid and urgent action to reassure the public and Labour Party members, but the panel is also clear that all its investigations must be conducted in a fair and equitable manner in accordance with Labour Party rules."
The BBC understands that neither Mrs Moran nor Mr Morley attended the panel's first meeting later on Wednesday.
Both MPs had been asked to appear before the panel but the party can not force them to attend.
Justice Secretary Jack Straw said the panel would "balance speed and fairness" but admitted it would not, in itself, restore public confidence which he said had been "unquestionably seriously damaged".
"In some ways, the relationship between voters and politicians has changed forever because of these allegations," he added.
He also hit back at suggestions Mr Cameron had taken the initiative on cleaning up the expenses system and reforming Parliament, arguing that Gordon Brown had proposed the "most significant and profound change in this area" with plans to end MPs' self-regulation.
But he added: "There will be days when the prime minister takes the initiative and days when David Cameron takes the initiative. That's politics."
In its first meeting, the panel of senior NEC members - Cath Speight, Ann Black and Sir Jeremy Beecham - began considering the allegations against the MPs who have been referred to it.
Former Labour Party secretary David Gardner says the public are tired of the expression "within the rules"
A statement issued by representatives of Ms Moran said she would not attend due to "ill health", but added that representation had been sent on her behalf.
According to the Telegraph, Ms Moran - the Labour MP for Luton South - spent £22,500 treating dry rot at the coastal property in Southampton she had designated as her second home, even though it was a two-hour drive from Parliament and 100 miles from her constituency.
Ms Moran has said she will pay the money back, but said she had stuck to the rules and acted in consultation with the Commons fees office.
Mr Morley, MP for Scunthorpe and an ex-environment minister, claimed £16,000 in interest payments on a mortgage that had already been paid off.
He has apologised and said he repaid all of the money once he had discovered his mistake, but Mr Brown has suspended Mr Morley from the Parliamentary Labour Party and also suspended the Labour whip from him.
I think the best thing to do, and I've said this to all my MPs, is to get out with your constituents, to hold meetings, to listen to them, to talk to them
David Cameron, Conservative leader
The Daily Telegraph said Dr Gibson claimed for a flat which his daughter and her partner lived in rent-free. It also claimed the Norwich North MP then sold it to them for less than he paid and well below market value.
Dr Gibson has insisted he acted within the rules but has offered to stand down at the next election if his constituents want him to.
The case of Mr Chaytor will be considered by the panel at a later date.
The Telegraph said the MP for Bury North claimed nearly £13,000 for a mortgage he had already cleared.
Mr Chaytor has apologised "unreservedly" for what had been "an unforgivable error in accounting procedures" and said he would arrange repayment to the Commons fees office immediately.
The Conservatives have launched their own scrutiny panel, which will decide if MPs have broken the rules and how much they should pay back.
But Mr Cameron said MPs who have made mistakes must say so.
He told BBC News: "I think the best thing to do, and I've said this to all my MPs, is to get out with your constituents, to hold meetings, to listen to them, to talk to them, to explain all of the circumstances of why we claimed what we claimed, why we did what we did".
He urged MPs to "hold up your hand if you made mistakes and got things wrong, and to start to rebuild trust in the political system, and in that link between the constituency and the MP".
He was speaking as the Tory MP, Julie Kirkbride, faces fresh scrutiny over her expenses with allegations she pays her sister £12,000 a year for clerical work - even though she lives more than 100 miles from her constituency in Bromsgrove, Worcestershire.
In its latest revelations, the Daily Telegraph, which has obtained the expenses claims of all 646 MPs, has also suggested that John Greenway, Tory MP for Ryedale, North Yorkshire, claimed £500 for petunias and fuchsia for his London flat.
And it turned the spotlight on MPs who claimed tax advice on their allowances.
It said that more than 40 government ministers were reimbursed a total of at least £25,000 for help with tax returns - but the paper said such fees were not tax-deductible.
It is unclear whether the MPs later paid any tax due, although Chancellor Alistair Darling said he had.
The costs of complying with the law are not an allowable expense against tax
Revenue and Customs spokesman
The paper said MPs had been given specific guidance from the taxman in 2005 that advice on self-assessment tax returns could not be regarded as a tax-free expense and were in effect a "benefit in kind".
A Revenue and Customs spokesman told the BBC that it was a "general principle of tax law" that accountancy fees connected with personal tax returns were not deductible.
Labour MPs have argued that tax advice relating to their work is a legitimate expense but the Tories say this is "completely wrong" and that any of the party's MPs charging the taxpayer for this will have to repay the money.
On Wednesday Downing Street said: "To the best of our knowledge, ministers do appear to have honoured their tax liabilities and will continue to do so.
"Obviously, we are in the process of checking whether ministers who are in this position are paying the tax that is due. We will obviously be making it clear to ministers that if there is any tax that has not been paid, it should be paid."
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