A potential for coronavirus cases to “reignite” remains as many adults are still unvaccinated, a former chief scientific adviser to the Government has warned.

Professor Sir Mark Walport, a member of the Scientific Advisory Group for Emergencies (Sage), told BBC Radio 4’s Today programme on Saturday that the country was on cusp of being able to loosen more restrictions.

But he warned that, with around 35% of adults not yet vaccinated, there was the potential for the “spark to reignite” and cases to rise again.

Prof Walport added: “We are on the cusp of being able to move to the next step of relaxation, it’s absolutely right that vaccines have been spectacularly successful but not everybody is protected.

“We’ve got 35% of adults who are not vaccinated and 60% who have only had one dose and the truth is the virus has not gone away.

“The mistake that has been made repeatedly really is relaxing just slightly too early. What we need to do is get the numbers right down, it’s important that we don’t act as an incubator for variant cases that might be able to resist immunity.”

He said there are still around 4,600 new cases a day across the UK, adding: “There’s the potential for that spark to reignite, it seems increasingly unlikely, but we need to get the numbers down.”

His warning comes after a club night pilot event in Liverpool – which saw around 3,000 clubbers return to the dancefloor at The First Dance, hosted by club night Circus, without social distancing or face coverings on Friday – was hailed as a “huge moment” in the journey to normality.

But while Culture Secretary Oliver Dowden also said that social distancing was being eased at the Snooker World Championships on Sunday and Monday, he stressed that any wider loosening of restrictions will be led by the data.

He added: “This weekend is another huge moment in our journey back to normality.

“Although this may seem like life getting back to normal these are science-led events, gathering valuable research as we leave no stone unturned to help us get back to the things we love this summer.

“We are making good progress but we have been clear that decisions on reopening will be led by the data. Our events research programme is playing its part in building up a crucial evidence base.”

New data revealed that up to April 30, nearly 15 million people in the UK had received a second dose of coronavirus vaccine.

The Government figures showed that that of the 49,287,257 jabs given in the UK so far, 34,346,273 were first doses and 14,940,984 were second doses.

Shadow health secretary Jonathan Ashworth on Saturday tweeted that he was “delighted” to get his first dose of the Oxford-AstraZeneca vaccine, and urged other people to get the jab when invited.

Meanwhile, The Department of Health and Social Care (DHSC) announced that surge testing will be deployed across parts of east London after several cases of the South African and Brazilian variants were detected.

It said that NHS test and Trace was working with Tower Hamlets Council to provide additional testing and genomic sequencing in targeted areas within the E1 postcode from Sunday.

The department said all the confirmed cases were self-isolating and there were no links between the new cases and the cluster of cases recently identified in the south London area.

The announcement comes as the Government said a further seven people had died within 28 days of testing positive for Covid-19 as of Saturday, bringing the UK total to 127,524.

Separate figures published by the UK’s statistics agencies show there have been 152,000 deaths registered in the UK where Covid-19 was mentioned on the death certificate.

The Government also said that care home residents will be able to spend time with loved ones in “low risk” visits without having to self-isolate on their return, after being threatened with legal action.

From Tuesday, residents leaving their home for a walk or to visit a loved one’s garden will no longer have to isolate for two weeks on their return.

But those leaving for medical appointments and for overnight visits will still be required to self-isolate for 14 days, the PA news agency understands.

The DHSC is expected to review the self-isolation requirement for more visits when it reaches the next stage of the Government’s road map on May 17.

The latest data shows that 95% of elderly residents have received one vaccine dose and 71% have received two.

The DHSC said updated guidance will be published in due course.

But John’s Campaign co-founder Julia Jones said the rule change did not go far enough, while Leigh Day partner Tessa Gregory, who is representing the campaign, said legal proceedings were due to be issued next week.

Elsewhere, the Department for Transport has missed a deadline set by MPs for grading countries under the new traffic light system for international travel.

Many people are eager to discover what countries are on the green list to avoid the need to self-isolate, as the ban on overseas leisure travel is expected to be lifted for people in England from May 17 as part of the next easing of coronavirus restrictions.

The Commons’ Transport Select Committee issued a report last week which stated that the green, amber and red lists of destinations must be published by Saturday “at the latest”, but the Government said the lists will be made public in “early May”.