Prime Minister David Cameron has been accused accused of "standing up for the wrong people" as charities warned that up to half a million disabled people and their families - including children and disabled adults living on their own - will be worse off under Universal Credit.

This, at the same time the Government was handing "huge tax cuts to 8,000 people earning over £1 million a year" from next April, according to a Labour MP.

An inquiry led by Baroness Tanni Grey-Thompson and supported by The Children’s Society, Citizens Advice and Disability Rights UK warned that cuts to the child disability additions and to the Severe Disability premium are likely to result in them struggling to pay for basic essentials such as food and heating.

It argues that three groups will be worse off including 230,000 severely disabled people who do not have another adult carer to assist them and 100,000 families with a disabled child.

Those without an adult to assist face losing up to £58 a week, while the Goverment's decision to halve the financial support for those with children could see families lose up to £28 a week.

One in ten families with disabled children affected by the changes feared losing their homes, according to the research.

However, it's the 116,000 disabled people in work - who could lose as much as £40 a week according to the charities - that has drawn particular criticism as it goes against the Government's stated intentions of "making work pay".

At present disabled people working more than 16 hours a week are entitled to the disability element of Working Tax Credit. However, under Universal Credit any person requiring additional support because they are disabled will have to take the heavily criticised Work Capability Assessment (WCA). Anyone who is found to be fully ‘fit for work’ in the WCA will receive no extra financial help within Universal Credit.

The tests, carried out by French firm Atos, have come in for huge criticism after a number of successful appeals against 'fit for work' decisions. It has previously been revealed that people with motor neurone disease, serious heart disease and even somebody with a broken back had been passed 'fit for work'.

The research found that many disabled people felt their health/impairment prevented full-time work and their health would deteriorate if they worked longer hours.

Yesterday in the House of Commons David Cameron was accused of standing up for the wrong people over the disability benefit cuts.

Labour MP for North East Glasgow Mr William Bain said: "Last week the Prime Minister promised that work would always pay, but this morning Baroness Grey-Thompson and the Children’s Society have revealed that his current plans for universal credit next year will mean that up to 116,000 disabled people in work could lose as much as £40 a week. Does that not say everything about how this divisive Prime Minister always stands up for the wrong people? At the same time as handing huge tax cuts to 8,000 people earning over £1 million a year he is going to penalise some of the bravest strivers in our country."

Cameron said the money that is going into disability benefits will not go down under Universal Credit; it will go up.

He said: "The overall amount of money will go from £1.35 billion last year to £1.45 billion in 2015. Under the plans, no recipients will lose out, unless their circumstances change. All current recipients are fully cash-protected by a transitional scheme. On future recipients, we have made an important decision and choice to increase the amount that we give to the most severely disabled children, and there will be a new lower amount for less disabled people. That is a choice that we are making. As I have said, we are increasing the overall amount of money and focusing on the most disabled. That shows the right values and the right approach."