WITH England's chief medical officer predicting another deadly “surge” of coronavirus across the country, there is a chance Boris Johnson's roadmap out of lockdown could experience some delays.

Chris Whitty warned “all modelling” suggests cases will soar as lockdown restrictions ease and rejected calls from MPs to ease lockdown restrictions faster.

"If you open up too fast, a lot more people die - a lot more people die," he said.

Whitty was joined by chief scientific adviser Sir Patrick Vallance who warned Parliament's Science and Technology Committee the reopening of schools could see the R number rise by 10 to 50 per cent.

And it's not just the top advisers to the Government warning there could be bumps in the road ahead.

The Prime Minister's hope, that by June 21 all restrictions could be relaxed with something close to normal life returning, is far from set in stone.

Here are five reasons why the lockdown exit 'roadmap' could be delayed, and to be cautious about making any big expensive plans.

Keep scrolling down for the key dates of the lockdown roadmap as it stands.

1 - Schools reopening could drive up infection rates

The professor who leads the Oxford vaccine team said children returning to school is necessary, but warned it will lead to an increase in Covid infections.

Sarah Gilbert, Professor of vaccinology at Oxford University, said this week: "We’ve got kids going back schools, and that’s absolutely necessary.

"But there may well be a slight increase in transmissions as a result of it.

"But if we can get the transmission rate down really low, then then we can cope with a small increase.”

2 - Covid surge likely if the UK opens up too quickly

Professor Chris Whitty said there were still risks to reopening society and the UK will experience another surge of cases at some point, potentially in late summer or through the autumn and winter.

Speaking to the House of Commons Science and Technology Committee alongside the Government’s chief scientific adviser Sir Patrick Vallance, Prof Whitty said the measures pencilled in for May 17, when indoor mixing of up to six people could be allowed, involved “significant risks”.

He told MPs he would “strongly advise” against any attempt to “concertina” the five-week interval between steps, saying the April 12 measures are “a very big block”, with shops and outdoor hospitality due to open.

May 17 further represents “a very significant block with a lot of stuff that is indoors for the first time, that is the point when we are really going to start to see some very significant risks accumulating, potentially”.

3 - The furlough scheme being extended until September

Chancellor Rishi Sunak said he's extended the furlough scheme for another six months because "things might change" in terms of easing England’s lockdown.

In his Budget speech last week, he announced furlough would continue until the end of September - more than three months after the June 21 date when all restrictions are currently due to end.

Mr Sunak explained this move was made to accommodate more "cautious views" of when the lockdown could finally be over - raising suspicions the public may have to wait longer than June 21 before all restrictions on social contact are removed.

Speaking on Good Morning Britain, he said: "We did that for a couple of reasons.

"I wanted people to have the reassurance that we were “going long”, beyond the end of the roadmap, because of course things might change."

4 - The speed of the vaccination programme

The Government’s aim is for the top nine priority groups – including all over-50s – to be offered their first jab by April 15 and for every adult to receive a dose by the end of July.

Vaccination rates slowed in the second half of February to around 2.3m a week due to a short-term dip in supply combined with stockpiling to ensure people get second doses within the recommended 12-week limit.

That dip in the pace could happen again, which might jeopardise Boris Johnson's plan for unlocking Britain.

However, the NHS is beginning to plan for a surge in doses from the middle of March.

A letter sent by NHS England to vaccinators on Tuesday promised that “from March 11 vaccine supply will increase substantially”.

5 - New variants

Scientists fear an infectious coronavirus mutation could prove resistant to current vaccines, forcing them to change the make-up of the doses.

This could delay easing lockdown by months.

If a vaccine resistant strain emerged, even people who have already had jabs could require booster shots.

If even the millions who have received a vaccine were again at greater risk, NHS hospitals would again be in danger of being overwhelmed.

However, new variants are "very unlikely" to send the UK back to square one, a top scientist said.

Professor Sharon Peacock, who is in charge of tracking strains of the virus in Britain, said the country is well equipped to "stay ahead" by adapting vaccines quickly.

The head of the COVID-19 Genomics UK scientific body told The Times she was "very optimistic" that immunisation would allow Britain to ease restrictions as planned.

The roadmap out of lockdown as it stands

March 8 - Schools in England reopened on Monday in step one of the Prime Minister's plan to ease shutdown restrictions.

March 29 - As part of step one, people will be allowed to meet outdoors in groups of six - or as two households if that number exceeds six - in time for Easter.

Outdoor sports facilities, such as tennis and basketball courts and golf courses, will be allowed to reopen.

Sports teams such as grassroots football will be able to resume.

April 12 - For step two, non-essential shops, personal care premises and public buildings will be allowed to reopen by April 12 at the earliest.

Outdoor attractions and settings can also reopen, including hospitality, zoos and theme parks.

The Government will make an announcement a week ahead of this stage to ensure it is safe to progress.

May 17 - Friends and family will be allowed to meet indoors again, but this will be subject to the rule of six or two households.

Pubs and restaurants will be allowed to serve customers indoors, concert halls, theatres and sports stadiums should be allowed to reopen.

June 21 - All legal limits on social contact can be removed and nightclubs can reopen as part of the fourth and final step of the roadmap.

Get more Salisbury news and nominate your local heroes for the South Wiltshire Hero Awards.

You can also like our Facebook page and follow us on Twitter and Instagram to stay up to date.

If you want online news with fewer ads, unlimited access and reader rewards - plus a chance to support our local journalism - find out more about registering or a digital subscription.

Email newsdesk@salisburyjournal.co.uk with your comments, pictures, letters and news stories.