A new proposed law will make it illegal for couples who live in different homes to meet for an indoor romantic liaision and then stay overnight during the coronavirus lockdown.
The Government's Health Protection Regulations had previously banned people leaving home without “reasonable excuse”.
However the new law which was laid before MPs on Monday said that “no person may participate in a gathering which takes place in a public or private place outdoors, and consists of more than six persons, or indoors, and consists of two or more persons”.
It defined a "gathering" as "when two or more people are present together in the same place in order to engage in any form of social interaction with each other, or to undertake any other activity with each other".
A separate provision made it illegal to stay overnight away from home “without reasonable excuse”, which could include moving home, work, attending funerals or providing care.
Downing Street yesterday insisted on Monday that police would show "discretion" and "common sense" in enforcing the law.
The proposed new law was reflected in new Government guidance yesterday which made clear that people cannot "cannot stay overnight away from your own home, except for in a limited set of circumstances, such as for work purposes".
It added that guests at garden parties will be risking a £100 fine if they poke around the householder's shed or garage.
New official advice published on June 1 offering the 'do's' and 'don'ts' as the coronavirus lockdown starts to ease stated that up to six people from different households can now meet outside in gardens or on roof terraces.
However the guidance - which is expected to trigger a surge in garden parties - warned that guests must remain outside and two metres (6.5 feet) apart - and they must not use the opportunity to look around a householder's garage or shed.
It said: "If you no longer want to remain outdoors, you should go home. Don’t go into garages, sheds or cabins – these are all indoor areas and where the risk of transmission is higher."
Guests at garden parties should also bring their own chairs for family barbecues and resist offers - however pressing - to borrow a tennis racquet for a quick knock-up with the host.
The guidance said: "You should not be sharing garden equipment with people outside of your household because of the risk of transmission.
"You could bring your own or if you have to use chairs, for example, you should wipe them down carefully with household cleaner before and after use.
"You should try to avoid shared equipment, for example you should use your own tennis racquet, golf club or basketball.
"Any equipment that is used should be cleaned frequently. Cleaning should be particularly thorough if it is to be used by someone else."
The Whitehall guidance also said that plunging into the host's swimming pool was also a no-no: "You should avoid using paddling pools and private swimming pools with people outside of your household."
Finally, staying the night with friends - even well-refreshed after an enjoyable garden party - was also banned. The guidance made clear that people "cannot stay overnight away from your own home, except for in a limited set of circumstances, such as for work purposes".
The guidance was contained in a new set of "Coronavirus outbreak FAQs" which sought to explain the Government's "plan to return life to as near normal as we can, for as many people as we can".
In general it said: "Public gatherings of more than six people from different households will be prohibited in law... There is no limit to the size of a gathering in an outdoor space if you are all members of the same household.
"Try to limit the number of people you see - especially over short periods of time - and be sure to stay two metres apart when you do."
The guidance warned it is illegal to organise a large party where lockdown rules will be broken saying: "It is a criminal offence to incite others to commit one of the above offences by e.g. inviting people to a party."
It also said that parents will not be allowed to turn a blind eye to Covid-19 rule breaking by their offspring with police allowed to instruct parents "to take steps to stop your children breaking these legal requirements again if they have already done so".
To drive home the message, penalties increased on Monday with police now able to issue fines of £100 for a first offence, rising to £400 for a third offence, £1,600 for a fifth offence and then up to a maximum penalty of £3,200.
The guidance said: "For both individuals and companies, if you do not pay your fine you could be taken to court, with magistrates able to impose unlimited fines."