More than 7,000 people have reportedly quit their membership of the Labour Party in the last week over the party's Article 50 stance.
Meanwhile, 4,000 people have joined the Liberal Democrats in the last month, pushing the party to its highest level of members for two decades, now soaring past 82,000.
The news comes as a senior Labour councillor in Tower Hamlets announced he is defecting to the Liberal Democrats due to Jeremy Corbyn's position on Europe.
Councillor Andrew Cregan revealed he is defecting becayuse he "cannot see Labour any longer as an unambiguously pro-Europe party"
Liberal Democrat Party President Sal Brinton said: "Labour under Corbyn have become cheerleaders for Brexit and are failing to provide a decent opposition.
"It's no surprise that so many former Labour members are voting with their feet and joining the real voice of opposition.
"They know we are now the only party fighting to prevent a damaging hard Brexit and to give the British people the final say on the deal.
"The Liberal Democrats will provide a home for all who want to stand up to this government and keep Britain open, tolerant and united."