Due to the covid pandemic the Government launched the Everyone in iniative. This means that the local authority will place you in a B&B or hostel. They will then continue to support you to find a permanent residence.
The Next steps accommodation programme (NSAP) the local authority will provide help and funding for you to get a permanent residence.
In order to claim benefits contact the local authority /job centre. You can use the job centre address or homeless charity etc as proof of address.
If benefits are stopped or sanctioned go to local authority who will help you by providing food and advice. You have to tell them that your money has been stopped otherwise they will not help you.
The Post Office and HSBC provide accounts for homeless people. You can use local job centre or homeless organisations as proof of address.
Register with a local doctor they have a legal duty to help you. Even if you have very little identification they can only refuse if they have full patient capacity. Many local authorities have set up walk in clinics.
Street link will help put you in contact with local services.