From the Shelter website
"Can I give the landlord notice and if so, how much?
If your agreement is periodic (ie rolling from week to week or month to month), you normally have to give at least four weeks' notice to end it, or a calendar month if you have a monthly tenancy. The only exceptions to this are:
If your landlord agrees to accept a shorter notice period (see above) or agrees that someone else can take your place (see below).
If you are an excluded occupier, in which case the amount of notice you have to give will depend on whether you have a tenancy or license agreement. Working out whether you have a tenancy or license can be quite complicated, especially if you don't have a written agreement. Get in touch with an adviser to check your rights if you can't agree a date that both you and your landlord are happy with. Use our directory to find a local advice centre.
If you pay rent less frequently than monthly (every three months, for example) - if this is the case, you have to give notice equivalent to a rental period.
It is always best to give notice in writing and ensure that the notice ends on the first or last day of the period of a tenancy. For example, if your tenancy is monthly and started on the fifth day of the month, the notice you give the landlord should end on the fourth or the fifth. Check with an adviser if you have any doubts about the dates. Use our directory to find one in your area."