HUNDREDS of thousands of Brits could get an extra £4,000 a year under the Government's trouble-hit Universal Credit system, the Sun Online can reveal today.

Around 700,000 claimants are in line for an extra £78 per week when they move on to the controversial new system, which has so far been hit by a string of teething problems.

Theresa May has told MPs that there are billions of pounds of unclaimed benefits sitting in a pot that will be able to be dished out automatically when Brits switch to the new system.

Three million people are set to go onto Universal Credit next year as part of a staged switchover from the current benefits system.

"700,000 people (will be) getting the benefits they are entitled to under Universal Credit."

And she added: "What we see in the changes we are putting forward is encouraging people into work and making sure work pays."

DWP sources told The Sun that under Universal Credit Brits might not have made an application for payments such as housing benefit - even though they may have been entitled to it.

But after people are moved on to the new system it will be easier to spot whether they are entitled to more money, and can submit claims for the extra cash.

An OBR report said this could be worth up to £4,000 per family - around £78 a week.

It estimates that by 2022/23, 200,000 of the 700,000 will be workers who aren't claiming the right amount of tax credits. The rest will be Brits who could claim more for child benefit, housing benefit, income support, jobseekers' allowance or ESA.

Those who are already on Universal Credit at the moment are only new claimants and are unlikely to be affected - but those who are claiming benefits on the old system and who will be rolled over soon could get a welcome boost.

Department for Work and Pensions Secretary Esther McVey told The Sun Online: "Universal Credit is a benefit system designed for the 21st century, replacing the old out-of-date legacy system.

"UC will provide more support to the most vulnerable, and helps people claim their right entitlement, helping those who may not be getting the right amount.

"As people move onto Universal Credit from the old system, there are around £2.4bn of unclaimed benefits that people will be able to access – benefiting around 700,000 people."

Dave Finch, Senior Fellow at the Resolution Foundation, said: "One of the key remaining advantages of Universal Credit is that by simplifying the benefit system it should help families to claim all of what they’re entitled to.

"This would offer a welcome income boost to over half a million families, but it risks being undermined by problems elsewhere – such as the large cuts made to support for working families.

"The government needs to both highlight the remaining benefits of Universal Credit, and do more to deal with the significant problems it still faces."

The news will be a boost for some of the millions of people who are set to migrate over to the new system, which aims to roll several benefits into one monthly payment.

But the flagship programme has been beset with issues so far, even though only a small number of the population are on it.

The system has been plagued with delays and problems, and hundreds of complaints that benefits have been slashed by hundreds of pounds a month.

Some were missing out on hundreds due to when their pay date fell.

And one family of a boy battling cancer were so poor on Universal Credit they were forced to eat his leftover hospital food.

The Sun Online revealed earlier this year the case of a disabled man born with 17 holes in his heart who has been denied benefits on Universal Credit - and told to get a job.

Ministers have insisted that no one will be worse off going on to the new system if their situation doesn't change.

But they will only be able to access transitional protection payments for a certain amount of time under Universal Credit.

Yesterday ex-Prime Minister Gordon Brown made a huge intervention in the debate, calling on ministers to halt the rollout.

He said that Universal Credit was forcing more kids into poverty, and demanded they rethink the entire system.

Ministers say the new programme will make work pay, and will encourage more Brits into work.