Lord Ashcroft's tax status continues to be questioned
A row has broken out over Conservative plans for a new law to guarantee the tax status of MPs and peers.
The Lib Dems say the Tories had repeatedly opposed their party's efforts to do the same thing.
Frontbencher Chris Huhne said it was "outrageous" the tax status of Tory donor Lord Ashcroft was still unclear.
But shadow Treasury minister Philip Hammond accused him of being more interested in a "political vendetta" than cleaning up politics.
On Sunday Conservative leader David Cameron announced that, if he became prime minister at the next general election, he would rush through legislation ensuring that all MPs and peers would "need to be, or be treated as, a full UK taxpayer".
Mr Cameron has been repeatedly questioned about the tax status of Lord Ashcroft - one of his party's biggest donors who has business interests in Belize.
Labour immediately denounced the plan as a "brazen attempt ... to obscure the truth about Lord Ashcroft's tax status".
Lib Dem home affairs spokesman Chris Huhne said his party had already tried to achieve the same result with three private members' bills.
He told the BBC Two's Daily Politics: "We have put forward this legislation on three separate occasions and we have not had support from either the Conservatives or Labour - because Labour has the same problem on this with Lord Paul."
He told Mr Hammond: "We and the Conservatives have a majority in the Lords so we could have actually got that through... you have on three occasions filibustered that bill. I am delighted that you have now seen the error of your ways."
He challenged the party to back upcoming Lib Dem amendments to the Constitutional Renewal Bill to bring forward the changes earlier.
Mr Hammond said his party had supported the "principle" of the Lib Dem private members' bills but said they did not adequately cover all the intricacies of international tax.
The Tory plans would "put beyond any doubt the tax status of legislators in the both the House of Commons and the House of Lords".
He accused Mr Huhne of playing "party political games" adding: "If it's going to be done it's got to be done properly."
When he was made a Conservative peer in 2000, Lord Ashcroft gave an undertaking that he would pay taxes in the UK but has since refused to comment on his tax status, insisting it was a private matter.