Britain has been plunged into a bleak midwinter as the twin crises of coronavirus and Brexit threaten to combine to create chaos.

France has blocked lorries from arriving in the UK due to fears over a new, potentially highly transmissible strain of coronavirus, giving a taste of what may be coming if there is border disruption after the end of the Brexit transition on December 31.

The UK imports many of its foods from Europe, and Sainsbury’s has warned the Channel shutdown could lead to shortages of lettuce, salad leaves, cauliflower, broccoli and citrus foods, while shoppers are being urged not to panic buy.

Boris Johnson has called a meeting of the government’s emergency Cobra committee to respond and he is facing growing pressure, including from Tory MPs, to take what appears to be the simplest option available and extend the transition period.

But the prime minister appears unlikely to agree, despite many seeing it as a pragmatic, sensible response to a once-in-a-century crisis.

Here’s why.

Why would extending the transition help?

The UK is currently following EU rules during the standstill Brexit transition period, which means it effectively remains a member of the single market and customs union.

That allows trade to continue to flow freely with the EU and, essentially, nothing major has changed since before we left on January 31.

Whatever the outcome of ongoing negotiations on a trade deal, there is likely to be disruption at the border from January 1 once that transition ends as businesses adapt to life outside the single market and customs union, including mountains of red tape and customs checks.

The government has said 80% of actions businesses need to take would apply in both deal and no-deal scenarios.

But there are widespread concerns that businesses simply won’t be ready – not least because they don’t know if there will be a deal or not and therefore do not know exactly what rules they will have to follow.

They have also been consumed with the Covid crisis this year.

And there are questions over the government’s own preparations, with vital infrastructure like lorry parks not yet complete and concerns over the readiness of border IT systems.

In September, Michael Gove warned that just 24% of firms felt fully ready, and outlined a “reasonable worst case scenario” including queues of 7,000 lorries in Kent if preparedness did not improve.

While the UK is effectively waiving import controls for the first six months of 2021, disruption of that scale at the ports could impact trade going both ways and lead to issues like food shortages.

Exporters could also face a huge economic hit if their products are snarled up in border delays, while just-in-time manufacturers may find it difficult to keep operating fully if parts cannot move back and forth across the border easily and quickly.

That’s why Tory MPs like Simon Hoare have called for the Brexit clock to be temporarily “stopped”, telling the PM it’s “time for maturity”.

Former cabinet minister Julian Smith meanwhile called for a “practical interim implementation period”, with a particular eye on Northern Ireland – which will be in a unique position from January 1, partially following EU rules and therefore dealing with new checks and rules.

London mayor Sadiq Khan has also broken from the official Labour line to call for a transition extension to protect supply chains and allow the government to give its “full and undivided attention” to the Covid crisis.

One argument for a temporary extension is the likelihood that an additional economic hit following a year in which the UK has suffered the worst recession in 300 years will delay recovery from the pandemic, and increase the demand on a government already operating in extreme circumstances trying to handle the Covid crisis and roll out the vaccine.

So why won’t Boris Johnson extend?

It all goes back to Johnson’s pledge to “get Brexit done”, which helped deliver his victory in the 2019 general election.

It is there in clear, bold type in the Tory manifesto of last December: “We will not extend the implementation period beyond December 2020.”

Despite having just months to conclude a trade deal after leaving the EU on January 31, 2020, the PM believed that delays simply put off the difficult trade-offs and decisions both sides had to make in negotiations.

And he felt that the process had dragged on too long since the 2016 referendum – an opinion undoubtedly shared by large sections of voters who propelled him to an 80-seat majority.

Key to Johnson’s refusal to extend the transition was also his belief that the UK could prosper without a trade deal, despite warnings that it would make the economic hit of Brexit even worse and slow down recovery from the Covid crisis. 

Johnson was also the choice for PM of hardline Tory Brexiteers, and would likely face a massive rebellion if he tried to get an extension through Parliament.

Keir Starmer’s reluctance to talk about Brexit after Johnson successfully portrayed Labour as frustraters of the process, and the PM’s expulsion of 21 MPs from the Tory Party last year for attempting to block no-deal also mean he has faced little pressure to change course.

And perhaps Johnson’s infamous prediction that the UK’s fight against Covid could allow a return to “normality” by Christmas blinded him to the dangers of the perfect storm of a winter surge in infections and Brexit chaos at the border.

On Monday, transport secretary Grant Shapps said extending the transition would “add fuel to the fire” of the situation by creating extra uncertainty for businesses.

But it’s a difficult line to hold when business lobby groups like the CBI are calling for, at the very least, “grace periods” to allow companies some breathing space.

Is extending the transition even possible?

Even if Johnson performed a U-turn and decided to extend, the legal situation is complex.

The withdrawal agreement (WA) signed by Johnson to take the UK out of the EU earlier this year specifies that the transition ends on December 31.

There was a legal opportunity to extend this by June 30 but, despite Covid, Johnson refused to do so.

It puts both sides in a tricky legal space that was outlined by the Institute for Government earlier this year.

One option would simply be to amend the WA, but this would force the government to recall parliament from Christmas recess amid London’s tier 4 coronavirus lockdown to pass primary legislation – and risking a huge rebellion from Brexiteer Tory MPs.

It would also “almost certainly” mean involving the European Court of Justice, according to the IfG, which is not a quick or easy process.

Another option is to agree a new transition period to begin on January 1, but this would mean “striking a new, complex agreement” and would need to be ratified by the UK and EU sides.

Again this would mean recalling parliament. 

A third option would be to agree an implementation phase as part of the wider trade deal currently being negotiated, but UK government sources say there are still “significant differences” between the two sides on that.

Finally, a temporary no-deal implementation phase could be agreed.

The EU has tabled emergency proposals to this effect but the UK is yet to indicate if it would agree.

Despite these hurdles, if there is political will to extend, it would likely be possible.

The EU is likely to accept, so the ball is firmly in Johnson’s court.