The hotel quarantine scheme launched by the Government has come under fire as travellers were left unable to book rooms just days before the policy is due to come into force.

The online booking portal went down shortly after it was launched on Thursday afternoon, and is not expected to be up and running again until around 10am on Friday.

The issue was branded “extremely worrying” by Labour, which said the system was “showing signs of failing from the outset”.

A spokesman for the Department of Health said the portal would be open “well before” the hotel quarantine scheme comes into effect, adding: “The website is currently undergoing work to correct a minor technical issue.”

UK nationals or residents returning to England from 33 “red list” countries will be required to spend 10 days in a Government-designated hotel from Monday.

Shadow home secretary Nick Thomas-Symonds said ministers must act urgently to get the booking website back up and running.

He said: “Over a year into this pandemic and 50 days on from the discovery of the South African strain, there are no excuses for yet more Government incompetence in the introduction of hotel quarantine.”

Rory Boland, Editor of Which? Travel, said the Government must ensure there are enough hotel rooms available.

He added: “If mandatory hotel quarantine is to be effective, it is essential the Government ensures there is enough provision of rooms to accommodate UK arrivals from red-list countries, to save anyone being left stranded abroad and significantly out of pocket for reasons beyond their control.”

Home Secretary Priti Patel said police patrols will be stepped up at airports and ports as the new hotel quarantine rules come into force.

People must fly into one of five specified airports, pay up to £1,750 for their stay and are “not guaranteed” the chance to leave their room for exercise, according to guidance published on Thursday.

Scotland, where every person arriving from overseas rather than just from specific countries will be subject to hotel quarantine from next week, will retain its tougher restrictions even if a UK-wide deal cannot be reached, First Minister Nicola Sturgeon said.

Meanwhile, ministers are reportedly set to discuss a Cabinet Office proposal on Friday to introduce vaccine and testing certificates for future international travel, according to Sky News.

Asked about the reports, a Government spokesperson said: “The UK Government, like most nations, wants to open up international travel in a responsible safe and fair manner and we continue to be guided by the science.

“We want to ensure there is an internationally recognised approach to enable travel and are working closely with international partners to do so.”

At the weekend, vaccines minister Nadhim Zahawi said state-issued immunity passports will not be given out – but those inoculated against coronavirus will be able to ask their GP for written proof of their vaccine status if needed for travel.

The Government said it is on course to meet its target of offering a vaccine to the estimated 15 million people in its top four priority groups – including frontline health and care workers and the over-70s – by Monday.

But MPs have warned that a lack of planning in Whitehall could affect the rollout of the next phase, with a target of getting the jab to the 17.7 million in the next five priority groups – including all over-50s – by the end of April.

The Commons Public Accounts Committee warned it was essential not to lose momentum and said ministers must ensure plans are in place to respond to potential future developments such as the need for an annual vaccination programme or the discovery of new variants of the virus.

On Thursday, Scottish Health Secretary Jeane Freeman said there will be a drop in vaccine supply across all four nations of the UK, caused by work being carried out by Pfizer – the manufacturer of one of the approved coronavirus vaccines.

But Wales has achieved its target of offering coronavirus vaccines to everyone in its first four priority groups.

First Minister Mark Drakeford said on Friday the milestone was a “truly phenomenal effort” for the country’s vaccine rollout, which has so far seen 684,097 people receive their first dose.

And Northern Ireland’s First Minister Arlene Foster said the vaccination programme there is approaching a “significant milestone”, with a quarter of all adults in the region expected to have received a first dose of a jab by the weekend.

We might still have advice and things, but actually legal restrictions on being able to meet the family and go out and things like that, I just don't think those are justifiable when you've protected the most vulnerable groups in society

With the vaccine rollout going well to date, Boris Johnson is facing pressure from Tories not to let the timetable for easing lockdown slip, despite warnings from senior scientists about the dangers still posed by the virus.

The Times newspaper reported that ministers are considering plans that would see social distancing measures stay in place until at least the autumn, with people wearing face coverings and keeping a metre apart for months.

Mark Harper, chairman of the Covid Recovery Group of lockdown-sceptic Tories, said keeping legal restrictions after all the over-50s and anyone over 16 with a health condition making them vulnerable to the virus have been vaccinated would not be justifiable.

He told the BBC’s Newscast podcast: “I think at that point, I don’t think you can justify legal restrictions at all.

“We might still have advice and things, but actually legal restrictions on being able to meet the family and go out and things like that, I just don’t think those are justifiable when you’ve protected the most vulnerable groups in society.”