Iain Duncan Smith will signal his determination to intensify welfare reforms, arguing that the crackdown on benefits is cutting unemployment.

The Work and Pensions Secretary and MP for Chingford and Woodford Green will use a speech in central London today to insist the Government is "delivering" after Labour left "whole sections of society on the sidelines".

The comments come amid speculation that the Tory general election manifesto could pledge to lower the benefit cap or extend other tough measures.

"The number of households where nobody had ever worked doubled - and the welfare bill rose by twice as much as average earnings," Mr Duncan Smith is to say.

"More than half of the rise in employment that we saw was accounted for by foreign nationals.

"And not just in London - three-quarters of Eastern European migrants in employment live outside London."

Mr Duncan Smith will argue that immigration into the UK has been a "supply and demand issue".

"Businesses needed the labour and because of the way our benefit system was constructed, too few of the economically inactive took the jobs on offer," he will say.

"When we took office, there were nearly five million people on out of work benefits.

"It was clear to me that in large part this situation was the product of a dysfunctional welfare system that often trapped those it was supposed to help in cycles of worklessness and dependency.

"My one aim as Work and Pensions Secretary has been to change this culture - and everything we have done, every programme we have introduced, has been about supporting everyone who is able to into work.

"The scale of the change has been enormous - but we are delivering, and it is changing our country for the better.

"Fixing society at the same time as the economy, matching a firm economic settlement to a firm social settlement; and in so doing putting this country on a path to a more productive, more dynamic, and ultimately a more contented, future."