Check out Shelters website, www.shelter.org.uk
or ring their advice line 0808 800 444.
Just to advise I know people have mentioned before but there is no legal requirement for a landlord to issue you with a written contract. Dont be concerned if nothing in writing because if you meet the requirements of a tenancy then you should be ok - these are:
Landlord and Tenant agreed
Property or room agreed
Exclusive Occupation - so that you have a room thats private or you have the entire flat.
Shelter also has a tenancy checker online that will tell you all about your rights.