Britain's opposition Liberal Democrat and Conservative parties opened talks today over a possible alliance to form a government following an inconclusive general election result.
The negotiations could give the Lib Dems their first taste of power for decades.
But grassroot party members, more left-leaning than the Lib Dem leadership and who have the power to scupper any deal, said they were unhappy about the talks with the centre-right Conservatives.
"I will never consider voting for the Lib Dems again if a Conservative/Lib Dem pact is the outcome of this election," said one supporter writing on an Lib Dem activist website. "A Lib-Con coalition means nothing and will do nothing," wrote another.
Lib Dem leader Nick Clegg spoke to his Conservative opposite, David Cameron, by telephone today ahead of broader talks between senior politicians from both parties.
The two men "agreed they should explore further proposals for a programme of economic and political reform", a Lib Dem spokesman said.
The Conservatives, who governed Britain for much of the 20th century but who have been out of power for 13 years, overtook ruling Labour to win the most parliamentary seats in yesterday's poll, but fell short of a majority.
The Lib Dems came a distant third, but now hold the balance of power.
With all 650 constituencies now declared, the Conservatives have won 307 seats (+98), Labour are on 258 (-91), the Liberal Democrats are on 57 (-5) and other parties have won a total of 28 (-1).
Mr Clegg, whose standing in his party has weakened after a disappointing poll result for the Lib Dems, meets with his newly elected legislators on Saturday.
The meeting will effectively form the first part of an intricate three-part internal process that limits Mr Clegg's powers when negotiating any form of coalition or support for another party.
The rules were imposed on Lib Dem leaders in 1998 by members angry after the disclosure of secret negotiations held with Labour which could have seen the two parties forming a centre-left alliance against the Conservatives.
The strict "triple lock" conditions mean it is much harder for Mr Clegg to agree a coalition than it would be for Mr Cameron.
The conditions state that any proposal that could affect the party's "independence of political action" must first win majority approval by Lib Dem legislators as well as the party's federal executive committee.
Unless that approval is passed by a three-quarters majority by both bodies, the party will have to call a special conference of members to discuss the plans, a event that would take at least a week to convene.
And if that assembly fails to pass the proposals with a two-thirds majority, a postal ballot of party members must be held.
In a statement outside 10 Downing Street earlier this afternoon, prime minister Gordon Brown said he was willing to open talks with Mr Clegg and other party leaders on forming a government. However, he said he respected Mr Clegg's position that he should first talk to Mr Cameron.
Mr Brown called for "far reaching" reform of the UK electoral system. "There needs to be immediate legislation on this to begin to restore public trust in politics," Mr Brown said. "A fairer voting system is central."
Despite Labour losing 90 MPs, Mr Brown said he wanted to play a part in the UK "having a strong, stable and principled government".
Additional reporting: Agencies