Sources in the Liberal Democrats have told ITV News that five new major donors - giving £50,000 each a year - have signed up in the past 10 days, including one who previously gave to the Conservatives.
The donors have each added their names to a group known as the Liberal Alliance that provide funds to specifically target Conservative MPs in so-called Blue Wall seats.
They include seats on the outskirts of London with populations that are getting younger and more diverse.
Sources said that two of the donors had approached the party out of the blue to ask if they could help.
It came as a multimillionaire former Tory donor - who gave £100,000 to Labour for the first time this summer - said he would never return to the party.
ITV News has heard how it's not just some of her own MPs who are calling for her to go -polls suggest half of Tory Party grassroot members want her out too. ITV News Deputy Political Editor Anushka Asthana reports
Gareth Quarry told ITV News that the Conservative's had "torn up" their reputation for fiscal prudence and said the damage was "irreparable".
He added: "I don't make this move lightly. This is changing the last 62 years of my life as a Tory supporter and voter. I don't do that lightly but I will never go back."
A Lib Dem source said: “We have seen a significant change over the past week with a dramatic increase in donors knocking at the door of the Liberal Democrats.
"They will not forgive the Conservatives for wrecking the economy and see us as the main party to unseat many of those MPs in their heartlands.
"They know there is little chance of getting the Conservatives out of power without us winning those seats.”
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