Staff members were inside the family-run Ship Inn at Cockwood, Devon, as the roof and wall behind the bar caved in due to torrential weather conditions.
The boozer is made from cob, a traditional West Country building material, which is a mixture of mud and straw.
Fortunately no one was injured, but it has left pub staff and patrons devastated.
It comes as Brits have been battered by wet and windy weather with more dreadful conditions on the way.
Forecasters have issued ‘danger to life’ alerts with Storm Ciaran set to bring torrential rain and 90mph winds.
Many have been told to expect persistent heavy downpours and flooding as the storm brings seven new yellow weather warnings across the UK.
Following the “shocking” disaster, Anna Brown, partner at the pub, said the family intended for the boozer to reopen as soon as possible after repairs, reports the BBC.
Mrs Brown said: “We’ve been here since 2007, this is our family pub and the wall, basically, at about half 11 this morning, the wall behind the the bar fell out, fell down in towards the garden.”
The business has closed until remedial works can be done.
And the family said they had been assured the wall could be repaired.
“We will be back and serving as soon as we possibly can,” Mrs Brown added.
And one visitor told DevonLive: “It looks like the council has shut off part of the road.
“We were walking our dog past the pub on Saturday and there was nothing wrong at all, but when we went past today – well, it’s all gone.”
Residents in the South West are being warned of “significant coastal flooding” amid heavy rain and strong winds.
Met Office meteorologists have put much of Britain under yellow weather warnings from yesterday until Thursday, November 2.
The Environment Agency has issued 72 flood warnings as the latest band of bad weather hits the country.
The Met Office has yellow warnings for rain in place on Sunday covering south Wales, south-east England, and eastern Scotland down to Newcastle.
New alerts were activated across Northern Ireland, Wales, and the south east coast as Storm Ciarán is set cause chaos into next week.
The most recent yellow weather warnings for rain on Monday cover Belfast, Swansea, Newcastle, Brighton and Portsmouth, as well as surrounding areas.
The Met Office warned Brits can expect “very strong and potentially damaging winds associated with Storm Ciarán possible on Thursday”.
Forecasters predict wind gusts of up to 90mph on the most exposed coast lines affected, while others will face 80mph gales.
Further in land, wind speeds are expected to reach between 50 and 60mph.