The Government is “eroding public trust” in Britain’s asylum system by over-promising and under-delivering with its controversial Rwanda scheme, MPs have been told.

The Refugee Council said the policy will not solve the problem of asylum-seekers making dangerous journeys across the English Channel, but is already resulting in “significant human suffering” for those awaiting removal.

Chief executive Enver Solomon told the Home Affairs Committee: “We had a Home Secretary who said to the public that she will make the route across the Channel unviable. It was totally unrealistic.

“We’ve had a Home Secretary who’s now said that the deal was Rwanda is going to solve the issue of people making dangerous journeys, which is an absolute issue that we are concerned about and we want to end as well. But it will not do that.

“So, if you over-promise and under-deliver, you erode public trust in the asylum system. And that is not what should be happening.”

Mr Solomon said dozens of people are thought to be in detention pending their removal to the central African country, while another witness said “disorientated” and “frightened” detainees are expressing suicidal thoughts and struggling to eat.

Theresa Schleicher, a casework manager for the charity Medical Justice, said one man served with a notice of intention to remove him was medically assessed and found likely to be lacking the capacity to understand his situation due to severe mental illness.

Some young people who say they are children have not been properly age-assessed, MPs were told, while some of those who have received notices of intent for removal are suspected victims of trafficking.

The Home Office was accused of “batting back” charities’ concerns.

Mr Solomon said: “We have seen children self-harming because they’re so worried and anxious about being sent to Rwanda. That can’t be what anyone wants to see as a consequence of this policy.

“And our grave concern is that, when we raised this with the Home Office, there didn’t seem to be any serious desire to exercise their duty of care, particularly in relation to children who are experiencing this extreme trauma and this extreme level of anxiety.”

The Home Office said it takes the welfare of people in its care “extremely seriously” and has robust safeguards.

MPs were told by a second panel of witnesses that it is “too soon” to say if the Rwanda scheme will deter people from making dangerous journeys across the Channel.

The numbers arriving do not seem to have changed much since the policy was announced, but the “jury’s still out” as nobody has yet been sent to Rwanda, said former Border Force director-general Tony Smith.

He called for more international co-operation to help the UK deal with small boat crossings, and said the UK needs to overcome political issues with France to get back round the table with them.

Asylum-seekers in Calais face “miserable conditions”, with a lack of support and significant police presence, Mr Smith said, adding: “The question is, if you’re going to stop the boats, how are you going to stop the boats?

“If you can’t persuade the French to behave in a different way, you have to deny them what they are seeking, which is settlement in the UK.

“And now, if the Rwanda model does start, and we do actually see publicly… that there is a possibility or even a likelihood that you may well find yourself not getting settlement in the UK, but you may find yourself in a third country, they may choose, despite their miserable conditions they’re in in Calais, not to come and to pursue their applications to remain in the EU, but I’m afraid I don’t know because it’s too soon to say.”

Another former immigration boss said “reasonable numbers” of people are likely to need to be removed to Rwanda if the policy is to deter asylum-seekers from making dangerous journeys to reach the UK.

David Wood, former director-general of Immigration Enforcement, said: “And then I don’t think there’s any prospect that all migrants will suddenly stop coming across the Channel.

“I think what it could do is maybe have an impact and reduce the numbers, but I think that they’re only likely to reduce if they see there is a real chance or risk of them, when they arrive in the UK, being taken to Rwanda.”

A Home Office spokeswoman said: “Our world-leading partnership with Rwanda is a key part of our strategy to overhaul the broken asylum system and break the evil people-smugglers’ business model.

“We take the welfare of all those in our care extremely seriously and have robust safeguards in place to protect vulnerable people.

“Nobody will be relocated if it is unsafe or inappropriate for them.”