Politicians have warned that the government is considering a “blanket ban” to prevent older people leaving their homes during the coronavirus crisis.

The health minister, Lord James Bethell, twice refused to deny that older people will be told to stay in extended lockdown in response to questions in the Lords on Wednesday.

“I was very concerned by the government’s refusal to answer my question,” said Lord David Blunkett, the former home secretary. “Older people must not be subjected to arbitrary incarceration as well as isolation.”

Blunkett asked Bethell what assessment the government has made of the impact of the restriction of movement on those defined on medical grounds as extremely vulnerable and what plans they have to change those restrictions.

“The more the government make restrictions age-related rather than risk-related, the more they risk people pushing back very heavily and refusing to keep to the rules,” he said.

“The government picked the arbitrary age of 70 out of the air back in March when they announced the initial lockdown based on age. Age is no longer a risk factor unless underlying health conditions are attached.”

Ros Altmann, the former pension minister, said: “I have real fears that ministers are considering blanket bans to prevent older people leaving their homes during the current crisis. Ministerial responses suggest government advisers may be seriously recommending using chronological age as a criterion for deciding whether people will be allowed to leave their homes.

“Such policies are normally the mark of authoritarian regimes, not a mature democracy. Collective punishment based on age should be no more acceptable than using gender, ethnicity or body mass index as defining factors.

“Blaming the virus is not a valid justification. These are conscious policy decisions. Isolating all older people, if others are allowed out, also risks damaging their physical and mental health.”

Bethell was forced to defend himself against accusations in the Lords from the former Labour energy minister Lord Truscott of a danger “that extending the lockdown for only certain groups might unintentionally discriminate against elderly and vulnerable people”.

Bethell was also unable to satisfy Conservative peer Lord Lucas, who asked: “Can we please ensure that vulnerable people have agency, that those who want to act as the unvulnerable are allowed to, that grandparents who wish to see their children are allowed to and, at the same time, that those who are young and vulnerable are protected in their decision to continue to isolate and are not discriminated against because of it?”

Bethell said: “It is an unfortunate fact that those who are medically vulnerable are singled out by the virus. We have to put in place measures to protect and safeguard their lives. It is the virus that makes this discrimination, not the government.

“On a personal level I completely understand where [Lord Lucas] is coming from. I have elderly relations who I would like to see, hold, touch and socialise with. But, as I said, I cannot hide from the house that this virus is an extremely predatory killer that has in its sights particular demographic groups, including the elderly and in particular those with conditions. It would be wrong of me to mislead the house by pretending that there was an easy way out of this epidemic for those who the disease seeks to attack.”

The Department for Health and Social Care has been approached for comment.