In a briefing to the public this morning (September 21), Sir Patrick Vallance, the government's chief scientific adviser, said the UK could see 50,000 new cases a day by mid-October without further restrictions.
The message comes amid murmurings prime minister Boris Johnson is considering stricter rules as the government attempts to curb the virus.
Professor Chris Whitty, the government's chief medical adviser, who also spoke at the briefing, said: "If we don't do enough, the virus will take off, and that is the path we are clearly on.
"If we do not change course, we will find ourselves in a very difficult problem."
Mr Whitty said the seasons were "against us" as the country faced the autumn and winter months, urging the public to look at the situation as a "six month problem".
Having partly priced in the anticipated speech, UK markets have fallen up to 4 per cent since opening this morning.
The UK's blue chip index has tumbled 3.5 per cent while the FTSE 250, more exposed to the domestic economy, is down 3.9 per cent.
Susannah Streeter, senior investment and markets analyst at Hargreaves Lansdown, said: "The prospect of evening coronavirus curfews, after a summer of recovering sales, is a bitter pill to swallow for the hospitality industry and that’s pushed Wagamama owner, The Restaurant Group, down by more than 18 per cent and pub chain J D Wetherspoon by almost 10 per cent."
Mr Whitty told the country it was a "very difficult balance" to protect both public health and the economy.
He said: "We know some of the things we have to do will cause significant impacts on the economy.
"If we do too little, the virus will go out of control. But if we go too far, we can cause damage to the economy."
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