Millions of people across the UK are preparing for tougher coronavirus restrictions amid growing concern about the rising number of cases.
Thirty-eight million people in the south and east of England will be living under tier three rules – the strictest measures – from Saturday.
Northern Ireland will begin a six-week lockdown from 26 December.
Wales had already announced a lockdown from 28 December which will be reviewed every three weeks and has no end date.
In Scotland, the government has warned that tougher restrictions – including a potential lockdown – after the festive period cannot be ruled out.
Official figures show infection rates went up in every region of England last week, apart from Yorkshire and the Humber.
From 00:01 GMT on Saturday, Bedfordshire, Buckinghamshire, Berkshire and Hertfordshire will move up a tier, along with parts of Surrey, East Sussex, Cambridgeshire and Hampshire.
Health Secretary Matt Hancock called the new tier levels in England “necessary”, and urged people to take “personal responsibility” for their actions to help curb the spread of the virus.
London had the highest rate, at 319.3 cases per 100,000 people in the week to December 13, up from 199.9 in the previous week. The rate went from 152.9 to 249.1 in eastern England, and from 167.6 to 238.7 in the South East.
It has prompted fresh concern about the decision by all four UK nations to relax restrictions and allow more mixing for five days over Christmas.
Ministers have issued updated guidance for the festive period but Dame Donna Kinnair, chief executive of the Royal College of Nursing, said it would “undoubtedly lead to more cases, more pressure on NHS and care services, and more deaths”.
London and parts of Hertfordshire and Essex had already been placed under the top level of restrictions earlier in the week.
Bristol and North Somerset will move from tier three to tier two, and Herefordshire will move from tier two into tier one.