I'm not quite sure what that clause actually means.
As I read it, "the temporary convenience of the Landlord only" may be an attempt to deprive you of your legal rights to remain in the property for a total of 4 years. Once a tenant has been in a property for 6 months, they are entitled to remain there for a total of 4 years without signing any other agreement other than the first agreement. This is called a Part 4 tenancy.
However, a Part 4 tenancy is not as secure as a fixed term agreement and a landlord may evict a tenant under certain conditions such as if the landlord wants the property for his own use or that of a close relative. Most of the 6 possible conditions have certain other conditions which the landlord must adhere to otherwise he will be in breach of the Notice of Termination and liable to pay damages to the ex tenant.
In my opinion, the clause in question would be invalid should a claim be brought against the landlord who tries to invoke the clause. You should get in writing exactly what that clause means. Just because a clause is in a lease does not mean that the clause is valid.