The Joint Biosecurity Centre of the British government on Monday raised the national Covid-19 alert level from three to four – the second highest – after new cases doubling every week prompted experts to envisage a scenario of 50,000 daily cases by mid-October.

Prime Minister Boris Johnson is due to make a statement in parliament on Tuesday to announce new measures to deal with the virus, seeking to strike a balance between ensuring public health and preventing further blows to Britain’s battered economy.

Before the statement, Johnson is expected to hold a cabinet meeting and a meeting of the emergency Cobra committee. A range of options have been discussed over the weekend with experts and ministers, with consensus reportedly veering towards more curbs instead of another national lockdown.

The alert level was reduced from level four to three on June 19, when new cases on successive days and weeks were recorded in the hundreds. They rose in the thousands in September, with 4,368 recorded on Monday evening.

The centre has five alert levels; the highest refers to a stage of outbreak in which there is a risk of health services being overwhelmed. The new current level four means the epidemic is in general circulation and transmission is “high or rising exponentially”.

The new level was agreed by the chief medical officers of England, Scotland, Wales and Northern Ireland, who said in a statement: “After a period of lower Covid cases and deaths, the number of cases are now rising rapidly and probably exponentially in significant parts of all four nations”.

“If we are to avoid significant excess deaths and exceptional pressure in the National Health Service and other health services over the autumn and winter, everyone has to follow the social distancing guidance, wear face coverings correctly and wash their hands regularly”.

“We know this will be a concerning news for many people. Please follow the rules, look after each other and together we will get through this”, they added.