Liberal Democrat leader Sir Ed Davey has accused the government of “stirring up fear and anxiety” by failing to provide enough detail about its welfare changes.

On Tuesday, the government announced a major shake-up of sickness and disabilities benefits, aimed at saving £5bn a year from the rising benefits bill.

Work and Pensions Minister Sir Stephen Timms said the changes would make the system “sustainable” and create a “substantial saving” but the Conservatives say the plans to not go far enough to cut spending.

Speaking to the BBC, Sir Ed did not say if he thought the cuts were too big or not big enough, but criticised ministers for creating uncertainty.

The government has not yet published an impact assessment of its plans, meaning it is not clear how many people will lose their benefits, their location and their circumstances.

Ministers have said the impact assessment will be produced at the same time as the Spring Statement on 26 March.

The Resolution Foundation think tank has estimated between 800,000 and 1.2 million people could lose support because of restrictions on claiming Pip.

Sir Ed said the current welfare system should be changed and that his party backed helping people into employment where possible, but also supporting those who unable to work.

“The problem with the government’s proposals is a lack of detail,” he said.

“What they’ve done is they’ve created a lot of uncertainty and a lot of fear.

“There are a lot of people out there caring after loved ones with disabilities – and they are really worried and really anxious because there has not been enough detail.”

Some of the changes will require new legislation, meaning MPs will be get a vote on the subject.

Asked if the Liberal Democrats would support the government, Sir Ed said: “We will look at the detail. We don’t know exactly what their changes are.

“We are very in favour of helping people in to work who can work – that’s the right thing.

“But stirring up all this fear and anxiety… that is the wrong way of going about it.”

The Resolution Foundation estimates that between 800,000 and 1.2 million people would lose between £4,200 and £6,300 per year by 2029/30 under the proposals.

During Prime Minister’s Questions, Labour MP Diane Abbott said there was “nothing moral about cutting benefits for what may be up to a million people” and accused the government of trying to balance the books “off the back of the most vulnerable”.

Sir Keir Starmer said it was a “moral issue” that one in eight young people were not in education or training.

“I am genuinely shocked that a million young people are in that position, and I am not prepared to shrug my shoulders and walk past it.”

Conservative shadow work and pensions secretary Helen Whatley said the changes were “too little, too late”.

She said the welfare bill was going up “so fast” and that the government “needed to be tougher”.