Birkenhead MP Frank Field has denounced his party's policy on tax credits while in power as "lunacy".

In an interview with the Spectator magazine, the former Labour welfare minister said his party removed the incentive for people to work while in Government.

And Mr Field, who has advised David Cameron on poverty, said he agreed with George Osborne's linking of the case of child killer Mick Philpott to the coalition's benefit shake-up.

Asked whether the Chancellor was right to make the link between Philpott and welfare, he said: "Absolutely. On all the welfare reforms, we're following the debate. We should be setting it."

He also launched a scathing attack on former prime minister Gordon Brown, describing him as a "fool" who "never really understood anything".

"What happened was this terrible tax credit subsidy - I think it was in 2008 - Gordon Brown, who never really understood anything, let alone the economy, changed the rules on how your child tax credits and child benefit were treated," he said.

"Up to that point, the monies you got for child benefit, and tax credits, were deducted from your social security payments so the bigger your child benefit, and child tax credits when you were in work, the bigger the incentive to work.

"But that fool, without by or leave, changed the rules... So this huge incentive to people with three or four children about working was lost. Lots of them to their credit have not responded to the lunacy of Gordon, and continued to work."

Mr Field himself linked the Philpott case to Labour's child benefit reforms, saying the killer was being paid hundreds of pounds whether he worked or not.

"I mean that terrible person who was wickedly controlling two women and their children, was earning hundreds and hundreds a week - he was getting that because it was child benefit that was paid whether he worked or not," Mr Field said.

Mr Osborne's comments about Philpott last month were met with a furious response from shadow chancellor Ed Balls, who described the Chancellor as "nasty and divisive" and said he had demeaned his office.

In the interview, Mr Field also said Britain should announce that it will only accept a certain number of migrants from Romania and Bulgaria once immigration controls are lifted.

"Once somebody breaches the dyke, I think others will follow," he said.