Three out of four pubs and other small businesses risk fines of up to £2,500 a day because they don't have the right insurance.
That is the stark warning from British Gas Business, which has released new research that shows millions of small firms do not have the compulsory Employers' Liability Cover in place.
This covers small businesses if an employee falls ill or is injured at work.
British Gas Business also said that half of the UK's small businesses were under-insured for the commercial activity they undertake. This leaves them exposed to possible financial losses and lawsuits.
"The recent summer floods have resulted in £3bn of claims from 50,000 businesses - many of them smaller businesses," said Neale Phillips, head of insurance at British Gas Business.
"Events such as these can interrupt trade for weeks, but inadequate insurance could spell the end of any small organisation.
"The financial implications of not having compulsory policies in place are also astronomical. I urge all small firms to check their insurance requirements today."
Federation of Licensed Victuallers Associations chief executive Tony Payne advised licensees to make sure they have insured the contents of their pubs for the amount it will cost to replace, not necessarily the amount for which it was bought.
The warning from British Gas Business comes as it launches a dedicated online business insurance comparison service for small firms called Insurance-for-Business.
The supplier said the service provides a route to a wide choice of business insurance from major insurers.
It offers instant cover for public and employers' liability, professional indemnity and more. See www.insurance-for-business.co.uk for more
information.