LORD Freud, the architect of the Conservatives' controversial welfare reforms, is to retire from the UK Government, Downing Street has announced.

While he won high praise from colleagues for his work in Whitehall, unions denounced him for introducing “poison” into the welfare system.

The 66-year-old peer will leave his role as a Work and Pensions minister at the end of December after the Queen approved his resignation.

He has served in the Department for Work and Pensions since David Cameron became Prime Minister in 2010.

Seen as one of the leading figures in the creation of the Government's flagship welfare reform, Universal Credit, he was promoted last year by Mr Cameron from a junior minister post to Minister of State.

Lord Freud first recommended wide-ranging reforms to the benefits system in 2007 and was later recruited to the Government to push through his ideas.

Downing Street said a successor DWP minister in the House of Lords would be appointed "in due course".

The peer, who has drawn no ministerial salary, is the longest serving Government minister in the same role, and the only one remaining in the same job from Mr Cameron's first round of appointments in May 2010.

He attracted controversy in 2014 after suggesting some disabled workers were "not worth" the minimum wage. He later apologised.

Announcing his retirement, Lord Freud said: "At the heart of our reforms is desire to give people independence to improve their lives. For too long, people have been trapped by a byzantine benefits system, leaving them powerless.

"This has always been my driving force; to give people back control over their own lives; to give support in times of need but also to give a clear route out of the benefits system and into independence.

"That's what universal credit does, and I'm incredibly proud of what we have achieved.”

Damian Green, the Work and Pensions Secretary, paid tribute to the peer.

"Everyone comes into government to make a difference but David's contribution to transforming the welfare system has been outstanding," he said.

However, the Public and Commercial Services union was less generous.

"Among staff in DWP, unemployed, sick and disabled people, there'll be no mourning the loss of a man who injected poison into our social security system,” declared a union spokesman.

"For years Freud has been at the heart of the cruel and dangerous upheaval of our employment and benefits services, and we'll be glad to see the back of him."

Meantime, George Osborne, the former Chancellor, paid tribute to his former colleague, saying: “David Freud was one of the brains behind our reforms that delivered record levels of employment. Thank you, David.”