Yes, the one year lease means nothing, they have an indefinite tenancy after 6 months no matter what the lease says. This has been the situation since 2004.
In fact, with the current rules the one year lease is a positive disadvantage to a landlord, you can't evict to sell during the one year period. So if you decide between now and this time next year that you want to evict to sell you won't be able to do so. Keep in mind also that it may be that all tenancies are converting to 6 year ones in March, we don't know, so you might decide to issue the eviction notice before that to cover yourself. If you've granted a one year fixed term tenancy, you can't do that.
It works like this:
1. If a right is given in legislation, you can't take it away in a lease, which is why the one year lease doesn't affect the tenants' indefinite tenancy.
2. You can always grant extra rights yourself better than what is in the legislations in the lease if you want to. A one year lease does this - you're giving the tenant extra rights, they cannot be evicted for the year unless there is a breach by them because you have promised them they can stay for the year. The lease is a one year fixed term one.
I think you may as well do the review now, though. I don't think that affects anything else.