Mr Miliband wants Labour to become again “the standard-bearer of the progressive majority” Labour leader Ed Miliband has appealed to disaffected Liberal Democrat voters to work with the opposition against the coalition government.
In a speech at the Fabian Society he said “thousands” of Lib Dems had now joined the Labour Party.
He also said he hoped the party realised that entering a coalition with the Tories was a “tragic mistake”.
And he said he was pleased many Lib Dems “now see Labour as the main vehicle for their hopes in the future”.
Mr Miliband also said he would not join in “gloating” over his party’s victory in the Oldham East and Saddleworth by-election.
That result saw Labour boosting its majority from 103 to over 3,500.
During his speech Mr Miliband said he wanted Lib Dems to “find a welcome home in our party, not just making up the numbers but contributing actively to the strengthening of our values and the renewal of our policies”.
He also said Labour must become again “the standard-bearer of the progressive majority”.
Mr Miliband said: “Forgive me if I decline to join those of you who are gloating at the expense of the Liberal Democrats.
“Their decision to join a Conservative-led government was a tragic mistake, and I hope they come to see that in time.
“But, equally, there are many Liberal Democrats who’ve decided to stay and fight for the progressive soul of their party. Most of them do not want to see their traditions sacrificed for personal ambition. I respect their choice too. And I understand how painful it is – and must be for them – to watch what is happening to their party.
“We do not doubt that they hold sincere views and we will co-operate, in Parliament and outside it, to fight with them against the direction of this government.
“In fact, it’s our duty to work with progressives everywhere… against what this government is doing.”
Writing in the Guardian, Mr Miliband earlier said he “respects the choice” of Lib Dems who have decided to stay and fight for the soul of their party.
In Thursday’s by-election, Debbie Abrahams finished 3,558 votes ahead of the Lib Dems with 14,718 votes. The party’s share of the vote increased from 31.9% to 42%.
But Lib Dem Elwyn Watkins fractionally increased the party’s vote share on the 2010 result from 31.6% at the general election to 31.9%.
The Greater Manchester by-election was called after a special court found ex-Labour minister Phil Woolas made false statements about Mr Watkins in May’s general election, in which Labour retained the seat by just 103 votes over the Lib Dems.
The ruling invalidated the result and resulted in Mr Woolas being barred from politics for three years.
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