Are they enforceable, and are they useful?
Enforceable? You can make any number of regulations and mostly, with varying degrees of protest, people will just do as they're told, and if you have to enforce the regulation the official letter from the secretary usually does the trick, even for the ultimate sanction of eviction. But you have to think that a tenant might one day refuse to do as they're told and defy you to do your worst so you want to be sure that at the end of the day a court will be happy to enforce your regulations.
It's questionable whether a probationary period is actually enforceable, though much depends on the kind of tenancy. I can't find anywhere that requires it to be so, but most of us have annual periodic tenancies which automatically renew until tenant or landlord gives the other notice to quit, and S.1 Allotments Act 1922 (as ammended) says notwithstanding anything the tenancy agreement might say to the contrary the landlord can't give less that 12 months notice. This precules a probationary period in a standard periodic tenancy.
However, I can't find anything to say that the landlord can't give the tenant a fixed term tenancy, say for three months, and when that expires satisfactorily the tenant would be elligable for a standard periodic tenancy. A fixed term tenancy automatically comes to an end so there's no notice to quit and the S.1 constraint doesn't apply. Thing is the tenant might successfully argue that despite the wording of the tenancy the fact is that the tenancy is a periodic tenancy and thus S.1 applies - the court will mostly take the view that if it walks like a duck and quacks like a duck, then it's a duck.
It needs to be a reasonably short fixed term or else you still can't do anything with a problem tenant, but it has to be long enough to give the tenant a chance.
Useful? I don't see what the problem is with the standard tenancy. The 1908 Act doesn't let you evict a tenant until at least three months whatever, and after that you only need to give the tenant reasonable time to comply with your regulations and then you can get them out and that doesn't seem any less easy than the probationary period. What a probationary period would appear to do is give the landlord an excuse to get rid of someone they just plain don't like, and that doesn't seem right. I'd have thought the fairest thing was for everyone, new tenants and longstanding tenants alike, to be held to the same reasonable standards.
What do you think?
