Councillor Knowles said his decision was about "party politics"
A Labour councillor in Wirral has defected to the Conservatives, hours after signing a declaration pledging loyally to his party.
Denis Knowles, a labour councillor for 13 years, said his "anguish with Labour as a whole" had prompted his decision at a council meeting on Monday night.
The Seacombe councillor had already signed his allegiance to Labour after an "ongoing dispute" with the party.
Council and Labour leader Steve Foulkes criticised his decision.
He said: "I deeply regret Councillor Knowles' decision to leave the Labour party and move to the Conservatives.
"Whatever he may say now, he has voted with the Labour group on all issues throughout the year and has not, at any stage, indicated his opposition to any Labour policies."
The Labour-led council has been heavily criticised for its decision to close 11 libraries, which prompted a government inquiry headed by culture minister Andy Burnham.
Council leader Steve Foulkes said he regretted the move
The Labour party claims Mr Knowles' defection was "directly linked" to him not being selected to sit on the Merseyside Passenger Transport Authority (MPTA) by the party.
Mr Knowles, however, said his exit was due to "party politics".
He added: "As a Labour representative the current situation with the party at national level has caused me sleepless nights.
"But I just want to do my job as a councillor and serve the public, I no longer feel I can do that under Labour".
Chief Conservative whip, councillor Chris Blakeley, said members of the party were delighted.
He added: "Denis and I discussed it and he said he was unhappy with the way his party were moving forward. He is a great ward councillor and the Conservatives are thrilled to welcome him."
Liberal Democrat Simon Holbrook, deputy council leader, said: "As a long established socialist and well known for his views it is a little surprising Denis should find a home with the Conservatives."
The defection means the Conservative party now has 25 seats on Wirral Council, Labour 20 and the Liberal Democrats 20.
It is a hung council with Labour and the Liberal Democrats in a joint partnership to take the majority.