The Crown Prosecution Service will reveal tomorrow whether any peers or MPs will face criminal charges over their expenses claims.
A spokesman said that an annoucement will be made by Director of Public Prosecutions Keir Starmer QC.
The Metropolitan Police is thought to have questioned some parliamentarians under caution, but no arrests have been made during their investigation of possible criminality.
In December the Met handed its conclusions to prosecutors, who must decide if any cases will go to court.
While none of those examined by the CPS have been named, media reports have focused on six MPs and peers.
They include Labour MPs Elliot Morley and David Chaytor, who both claimed second home allowances on homes that were mortgage-free.
Another Labour MP, Jim Devine, has been accused of submitting for electrical work worth £2,157 from a company with an allegedly fake address and an invalid VAT number.
Chaytor is scheduled to present his private member's bill on local authorities in the Commons tomorrow morning.
Labour peer Baroness Uddin has been accused of claiming for a second home she never used.
Lord Clarke of Hampstead, a former chair of the Labour Party, has admitted to claiming up to £18,000 a year for overnight subsistence when he often stayed with friends in London or returned home to St Albans.
Tory peer Lord Hanningfield has been accused of claiming overnight allowances of £100,000 when he was in fact returning to his home.
Those accused could be prosecuted for fraud or false accounting, which carry maximum sentences of ten or seven years in prison.
Today MPs were ordered to repay a total of £1.12m in second home expenses following an audit of their past claims.
Sir Thomas Legg recommended that 390 MPs repay a total of £1.3m, with almost £800,000 having been repaid since April last year.
But the appeals process overseen by former judge Sir Paul Kennedy cut the repayments demanded by £185,000 to a total of £1.12m.
The long-awaited report into Westminster's expenses scandal criticised the "deeply flawed" House of Commons system.
It shows which MPs have had their expense repayments reduced, many of whom have already made their appeals public.
The Legg report found that 48 per cent of the 752 MPs whose expenses were examined have '"no issues" with their expenses, but three have been told to repay over £40,000.
The highest single repayment demand following the appeals process has been made of junior communities minister Barbara Follett who must pay a total of £42,458.
Dods Parliamentary Communications Ltd