This is very tricky situation, as current Covid restrictions do not allow for mixing between households. It is also very difficult to ‘inform’ on housemates.
The first option, of course, is to try to persuade your housemates not to have a party, or have friends around, since in lockdown this will mean breaking the law.
If this is not successful, you will need to demonstrate that you are not part of the gathering, and this is unfortunately open to interpretation;
If the Police call at your house and find you in your bedroom watching TV or asleep, they may decide that you are not part of the gathering.
You could decide to contact the Police ahead of a planned event, to let them know that a party is planned, and that you are not a part of this. The Police are likely to contact the house in advance and say that they have heard about the party through e.g. social media – and they will not mention the tip off has come from you. To do this, you can contact Northumbria Police via their email firstname.lastname@example.org
If you are in your house and a party starts, you could call Operation Oak to let them know that there is a gathering at your house, and that you are not involved. If this is a noisy gathering it is likely that it will be reported by somebody else anyway. In contacting Oak, you can give your name and ask that this is not disclosed. The number for Operation Oak is 07504 898148.
The Government has introduced a £800 fine for people attending house parties, which can double for each offence up to a maximum of £6,400. This will apply to anyone who attends illegal gatherings of more than 15 people from outside their household.