No, sorry for confusing things, just thought there was a good learning point for anyone else who's been renting since before the new law... make sure you have an agreement.
Clearly they didn't put me on another fixed term if they didn't actually change the tenancy agreement. Looking back, it seems obvious, but I don't think I've ever received another agreement after the initial one and I've rented for around 18 years.
So what was the £40 for? They've either renewed your tenancy, or you've been giving them £40 for nothing.
At the end of your initial fixed term, what normally happens is one of 2 things:
A) You automatically go on to a periodic tenancy - you can give one month's notice, landlord can give 2 months - they shouldn't be charging you if this is the case, since it requires 0 effort on their part, they especially shouldn't be charging you 6 monthly/annually.
B) You renew your tenancy for another fixed term - you may be charged for this, as it involves the agency clicking a few mouse buttons.
Given that they have been charging you to renew the tenancy, it implies that they have been renewing the tenancy - as I mentioned, they don't necessarily need to provide a new tenancy agreement if the terms are the same as the old one, so the fact they haven't got a new version is irrelevant. What is relevant is the fact they have been charging you to renew.
The court case I linked is relevant because:
The ramifications of this ruling imply that ALL FIXED TERM tenancies coming to an end create a NEW contract.
Meaning your new tenancy commenced at the point of the most recent "renewal", and the legislation in place at that time would apply.
I'd ask the agent exactly what you were paying that £40 for if it wasn't to renew your tenancy, if they then admit they haven't been renewing your contract, I'd be demanding a refund of your £720/£1440 (18 years worth of £40 non-existent "renewals").
If they do state they've been renewing your tenancy, then see above - make sure you get this in writing.
I'll also point out at this point that I'm in no way a legal professional, but based on logic, this is how I would approach the situation.