Nick Clegg, David Cameron and Gordon Brown attend the VE Day 65th anniversary tributes at the Cenotaph in London on Saturday
A senior Welsh Liberal Democrat says his party could go into government without a deal on electoral reform.
Lord Carlile said it was naive to think there had to be an agreement on proportional representation (PR).
The ex-Montgomeryshire MP stressed he is not involved in the talks, but said while PR must be on "on the table", Lib Dems will look at the "bigger picture".
Plaid Cymru do not rule out talking to the Tories but say they are only preparing for discussions with Labour.
Lib Dem leader Nick Clegg has met senior Lib Dems to discuss the Conservative offer after Tories won most seats in Thursday's general election.
Mr Clegg has also spoken by phone to Gordon Brown, who remains prime minister, and has invited the Lib Dems to talk to Labour, if talks with the Conservatives fail.
It is also possible that Plaid could play a role in a deal. However, while the Scottish National Party - who have formed a "Celtic bloc" with Plaid - have ruled out an arrangement with the Tories, Plaid have not.
Lord Carlile, who as Alex Carlile represented Montgomeryshire from 1983-97, said it was "completely naive" to approach the "present crisis" thinking there would be no deal without an offer on PR.
"PR is an important future prospect, [a] major plank of policy for the Liberal Democrats, but if the national interest requires that we have to sort out more immediate questions first, then that is what the Liberal Democrats will do," he told BBC Wales.
Lord Carlile emphasised that he was not involved in the discussions, and did not know any details, but believed Lib Dem' negotiators' main concern was "the national interest and ensuring that we have a stable government".
'Cleaning up politics'
"What I believe as a senior Liberal Democrat is that though PR will have to be on the table and dealt with in a meaningful way, if there are more important immediate requirements they will be dealt with first: a commitment to do something serious about cleaning up politics, the electoral system, making votes count more meaningfully, is very important to the Liberal Democrats, but it's only part of a bigger picture, as Nick Clegg has made clear."
He also urged the party to support their leaders. "The one way to let Nick Clegg and the leadership down very badly is to force a long drawn-out process. There isn't time".
The Tories secured 306 of the 649 constituencies contested on 6 May, leaving them short of the 326 MPs needed for an outright majority.
Labour finished with 258 MPs, down 91, the Lib Dems 57, down five, and other parties 28, including three Plaid Cymru and six SNP.
Welsh Secretary Peter Hain has insisted it would be possible for Labour to form a government with the Lib Dems and push through reform, even though the two parties together are not able to command a majority.
Mr Hain said there was a "progressive majority" in the Commons that included other small parties.
Plaid parliamentary leader Elfyn Llwyd told Good Morning Wales said his party had been assigned a civil servant by Labour to arrange discussions.
SNP leader Alex Salmond has said he would not speak to the Tories, and Mr Llwyd was asked if he would do the same.
Mr Llwyd said Mr Salmond had "more or less" ruled out Tory discussions on Friday "in an unguarded moment," but insisted Plaid and the SNP were "as one, talking about a discussion with the would-be Labour administration".
Mr Salmond has also called on Lib Dems to join a "progressive alliance" involving Labour, the SNP and Plaid.
Plaid are already in coalition with Labour in the Welsh Assembly Government, but Mr Llwyd said there was never any question of following suit at a UK level. He said any deal would be on a case-by-case basis.
Asked if he would "slam the phone down" if Plaid were contacted by the Tories, he said a democrat would not do that.
"We haven't ruled anything in and anything out, and if and when we come to a position where we acknowledge that we cannot come to an arrangement with Labour that will be another day for consideration."
Plaid leader Ieuan Wyn Jones said on Friday that they were "prepared to talk" to any other parties to get a "good deal for Wales".