As lodgers are 'excluded occupiers', they have less rights than a tenant. An excluded occupier means that you don't need to give the lodger a form or eviction notice to get them to leave.
The landlord should give the lodger 'reasonable' notice to leave. Notice can be given verbally; it doesn't need to be in writing. The lodger must leave when the notice period ends. For example, if you give a verbal notice to the lodger to leave in 2 weeks time, then they must leave in 2 weeks time.
If there is a written agreement (such as a Lodger agreement) it should say how much notice you need to give. If there is no lodger agreement, then you should give 'reasonable notice'. This can depend on how often the rent is paid. You don't have to give the lodger notice in writing unless the agreement says you should.
Notice is not required if the landlord and lodger both agree to end the lodging arrangement. The process is relatively straightforward and the landlord doesn't need to serve any eviction notices or forms. If both parties agree, you can simply record this in a document stating that the lodger has agreed to leave.
For more information on evicting lodgers in England and Wales, read How to evict a lodger.
If you are a homeowner in Scotland, you must give your lodger notice to quit at least four weeks before you want them to leave. The lodger must leave when the notice period ends. For more information, read Evicting lodgers in Scotland.