LONDON- Britons who flout the government's instructions to stay at home face on-the-spot fines of 30 pounds ($35) which could rise significantly if needed, Prime Minister Boris Johnson's spokesman said on Tuesday.

On Monday, Johnson said Britons would only be allowed out to shop for basic necessities, exercise, for a medical need, to provide care or to travel to work where absolutely necessary. Gatherings of more than two people in public who do not live together are banned. 

"Regulations will be made as soon as possible and by Thursday at the latest to allow the police to issue fines to those who refuse to comply," the spokesman said, adding police would "take whatever steps they consider approporiate to disperse groups of people who are flouting the rules".

The spokesman said those ignoring the rules would initially be fined 30 pounds but this amount would be kept under review and could be increased "significantly if it is necessary to ensure public compliance".

(Reporting by Kylie MacLellan; editing by Stephen Addison) ((kylie.maclellan@thomsonreuters.com; +44 207 542 0401; Reuters Messaging: kylie.maclellan.thomsonreuters.com@reuters.net))