If you issue a S21 at the beginning of the tenancy, are you not telling the tenant that he has to vacate on or before the termination date of the contract? It seems to me that he could then leave at any time before termination date without giving you any notice. Possibly, a third party would see this as contradictory. Mind you, there are different opinions on this and it would be interesting for some clear cut guidance.
I would prefer a 12m AST with a 6m break clause, rather than a 6m AST, which could mean that you get a number of temporary tenants - may not be particularly good for the decoration.
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