Boris Johnson has said “we are tantalisingly close” to lifting the final swathe of coronavirus restrictions as he prepares to address the country to confirm whether the next stage of unlocking can go ahead.

Prime Minister Boris Johnson is expected to say that the country can move to Step 4 of the road map to lift measures but also warn that Covid-19 cases will rise as rules designed to suppress the virus are removed.

Mr Johnson will host a press conference on Monday afternoon, while Health Secretary Sajid Javid will announce the plans in Parliament.

Downing Street said the unlocking would be based on four tests – the success of the vaccine rollout, evidence that the vaccine is causing a reduction in hospitalisations and deaths, that infection rates do not risk a surge in hospital admissions, and that no new variants of concern throw progress off track.

The PM said: “We are tantalisingly close to the final milestone in our road map out of lockdown, but the plan to restore our freedoms must come with a warning.

“While the phenomenal vaccine rollout has offered every adult some protection against the virus, and the crucial link between cases, hospitalisations and deaths is weakened, the global pandemic is not over yet.

“Cases will rise as we unlock, so as we confirm our plans today, our message will be clear. Caution is absolutely vital, and we must all take responsibility so we don’t undo our progress, ensuring we continue to protect our NHS.”

Moving to Step 4 was delayed by four weeks to ensure all adults had been offered a vaccine, and as of Friday 80.3 million vaccine doses have been administered in the UK, with 45.7 million adults receiving a first dose (86.9%) and 34.5 million adults receiving both doses (65.6%).

Analysis from Public Health England (PHE) and the University of Cambridge suggests that vaccines have so far prevented an estimated 8.5 million infections and 30,000 deaths in England alone.

Downing Street also said the delay has meant the end of restrictions is closer to the school holidays, where transmission rates are expected to be lower.

But it also suggested that waiting even later in the year to reopen could put more pressure on the NHS as the health service contends with winter illnesses such as flu.

On Sunday, vaccines minister Nadhim Zahawi told The Andrew Marr Show on the BBC: “One of the things that we’ve done, obviously, we’ve got the vaccination programme, but we’re already planning… the NHS is planning for co-administration of the Covid boost starting early September, with flu, because we’ve had very little flu circulating in communities because of the lockdown.

“So one of the big risks that I and others were worried about is in a bad flu season, you could see 20,000 people dying.”