Former Labour assembly member Alison Halford has joined the Conservative Party.
Alison Halford says she wants to play her part helping the Tories
Ms Halford, 65, once Britain's highest-ranking woman police officer, was AM for Delyn between 1999 and 2003.
Ms Halford, who will advise Tories on policing and social justice matters said: "I have been disillusioned with Tony Blair's leadership."
A Welsh Labour spokesperson said Ms Halford's former constituents would not forget "Tory misrule in Wales".
Ms Halford will advise Shadow Welsh Secretary Cheryl Gillan on policing matters, including the merger of the four Welsh forces.
She will also advise Tory assembly group leader Nick Bourne and policy director David Melding on policy, particularly on social justice issues.
Ms Halford, from Flintshire, joined the Labour Party in 1994 after a 30-year career in the police in which she rose to become assistant chief constable of the Merseyside force.
She stood down from front-line politics at the last assembly election in 2003.
She said: "I left the Labour Party over the issue of cronyism when Peter Mandelson was given yet another chance by being appointed a European Commissioner.
"Trust in politicians is important and I have lost all faith in the prime minister."
"It is now time for Labour to go and for the newly-led, more compassionate Conservative Party to be given the chance to govern.
"I want to play my part in helping the Conservative Party achieve this important objective."
She added: "I very much look forward to working with Cheryl Gillan and Nick Bourne, whom I have always held in high regard."
'Out of touch'
Nick Bourne, the Tories' leader in the assembly, said he was "delighted" Ms Halford had joined the party.
He added: "She has had distinguished careers in the police force and as an assembly member and is a person who rightly commands the utmost respect.
"Alison's decision to join the Conservatives is further evidence of the progress the party is making under David Cameron's leadership.
"The fact that people of Alison's calibre and background have joined the Conservatives is a clear sign that Tony Blair's Labour Party is increasingly out of touch with the British public."
Ms Gillan said she was "looking forward" to working with Ms Halford.
A Welsh Labour spokesperson said: "Alison Halford will have her work cut out advising the Conservatives on social justice.
"The party of which she is now a member gave Britain three million unemployed, two recessions and massive cuts to front line public services.
"Alison may look back through rose-tinted glasses at the 18 long years of Tory misrule in Wales, but the people she used to represent won't so easily forget."