Short Term Lodger Paperwork

Tenancy Types and Management

My son is looking to go away travelling for 5-12 months in September, and as such is considering renting out rooms in his house whilst keeping his room and en-suite locked so he can come and go as required should he come back sooner or between trips.

The question he asked me was what type of tenancy/licence/agreement should he put in place, how easily can he end those arrangements when he returns and any other pitfalls.

Likely income would cover mortgage costs and bills on the assumption he lets rooms on an inclusive basis. 

He hasn't considered lender consent or otherwise.

Worth doing, or not worth the (potential) hassle for less than a few thousand.

All input welcomed!