The flouting of Covid restrictions over Christmas and New Year will lead to a spike in cases, Hertfordshire's public health chief has warned.

Director of public health Jim McManus, said cases were now rising in every part of the county – with the new variant accounting for 50 per cent of infections.

He warned that despite the announcement of the latest lockdown, the surge in cases – now concentrated in the working age population – would continue for at least a week, before it would reduce.

Pointing to evidence of house parties, to demonstrations without face masks and crowded alcohol aisles in supermarkets, he said there was "no doubt" that there would be a spike in infection from the Christmas and New Year period.

But he says that sticking to the restrictions could lead to a halving in the infection rate within 28 days – easing pressure on the NHS and speeding up the vaccination programme, which he says is the 'number one priority.

"The longer we fail to social distance and take precautions, the longer we will be in lockdown and the more risk we will get variants which can evade the vaccine," said Mr McManus.

"If we want out of lockdown we have to behave as if we and everyone else we meet outside our homes are infected.

"The longer the virus circulates, the more NHS staff will get sick, have to self isolate or care for those who are sick, and the longer it will take therefore to get the vaccine rolled out to everyone.

"If we halve the infection rate we can reduce hospitalisations by up to 30 per cent which means more NHS staff can focus on vaccination.

"We can halve the infection rate in 28 days if everyone adheres to the measures."

But sticking to lockdown restrictions for 28 days, he says, could see infection rates in the county fall by half.

Latest data shows that in the past seven days (to January 6), 9,994 people in Hertfordshire have been diagnosed with Covid – that's a rate of 840 per 100,000.

And the data shows that (as of December 30) there are are more than 400 patients being treated for Covid in Hertfordshire hospitals (285 in West Herts hospitals, 120 in The Lister and 174 in Princess Alexander).