Lockdown fines will rise to £100 in England from Wednesday for people found to be breaking the rules.
But the first fine someone receives, if police believe they are flouting restrictions on movement during the coronavirus outbreak, will be lowered to £50 if paid within 14 days, according to the Home Office.
Fines will double for each repeat offence, up to a maximum of £3,200.
Existing legislation known as the Health Protection (Coronavirus, Restrictions) (England) Regulations 2020 will be updated from Wednesday to reflect the changes coming into force.
It is not yet clear if the same changes to fines will be adopted in Wales, Scotland and Northern Ireland.
The news comes as the body that represents police officers warned the Prime Minister's relaxed lockdown guidance still risks being a set of "loose rules that are left open to interpretation" and is difficult to implement.
John Apter, the national chairman of the Police Federation of England and Wales, said: "What we need from the Prime Minister and the Government now is clear and unambiguous messaging and guidance, explaining what exactly is expected of the public, so that my colleagues can do their level best to police it.
"Police officers will continue to do their best, but their work must be based on crystal clear guidance, not loose rules that are left open to interpretation - because that will be grossly unfair on officers whose job is already challenging."
Mr Apter said Boris Johnson's statement came after a week of "mixed messages and the release of some information which, fuelled by media speculation, meant many people acted as though the lockdown had already ended".
He said: "If the message of what is expected of the public is not clear, then it will make the job of policing this legislation almost impossible."
It comes after the Metropolitan Police Federation (MPF), which represents police officers in London, criticised the Government's pandemic response as "wishy-washy" amid concerns that the public had begun ignoring lockdown restrictions.
MPF's Ken Marsh told BBC Radio 4: "It's been quite wishy-washy how we've gone about it.
"Had we been very stringent from the off - it is painful, but it's not overly painful in terms of what you're actually being asked to do - then I think we would have a better result now."
