Ending Tenancy Early When It's a Fixed 1 Year Contract

Tenancy Types and Management

I am using the RLA AST. It's a 1 Year tenancy with no break clause. I usually have a break clause but on this occassion I did not. Currently 7 months into the tenancy. I recently had cause to enter the property (legally) and in my opinion the tenant has broken the terms and conditions. I am referring to clause B4 "You must keep the inside of the property in at least as good a condition as it was when the tenancy started (fair wear and tear excepted)." and a clause I added about smoking which the tenant has clearly disregarded.

The question I have is can I serve the tenant with a Section 21 notice now on the basis that he has broken the terms and conditions or do I have to wait until 10 months have elapsed and then inform him that the tenancy will not be renewed and serve the Section 21 at this point in time.