You have been the victim of the crime of unlawful eviction. Call the police on on 999 immediately.
There may be other action you can take but your first step should be to call the police to assist you. I assume your landlord has no possession order.
No it isn't. Illegal eviction is a crime and you are a victim of that crime. Go to your local police station, tell them what has happened insist on making a complaint and if they refuse demand to talk to a more senior oficer
Follow this link for the Shelter website section on ilegal eviction. http://england.shelter.org.uk/get_advice/eviction/harassment_and_illegal_eviction_by_landlord/illegal_eviction Thi sets out better than I can the legal rules for the stuation you are in.