Thanks for all the replies guys 
I agree that if I were in the tenants shoes I would also be thinking that I've signed for 12 months and so I'm staying for the 12 months. I do plan to go after the agents as they have also failed to pick up on a number of (albeit minor) breaches by previous tenants. There is a slight problem in that a lot of the arrangements between my wife (was my GF at the time the first resident moved in) and the agents seems to have been verbal. I'm still waiting for a full copy of the agreement with the Agent. We had previously asked that all leases be on 6 monthly terms as due to the nature of our contracts out here, we could move back at relatively short notice. We also asked the agents to forward an electronic copy of correspondence to us so that we could act upon any issues within the required notice period, but they seem to do this 'willy nilly', I'm going to ask for a copy of our file showing all correspondence.
Anyway, do you think it worth talking to the tenant to see if they're negotiable on the tenancy end date? Especially if we got the agents to find them an alternative property and offer to pay their moving costs? I'm concerned that if we contact them to try and negotiate an early end, that it may be seen as harassment.
It looks like we'll end up renting for the 6 months, but just a pain as we had plans to give the place a makeover over the xmas period. Having said that, we're also keeping an eye on a couple of flats in need of renovation in the same area