It's a difficult question.
Simple answer: No Sally. It's an implied term of your tenancy agreement that the landlord provides you with access, and that means 24hours a day. If the landlord won't listen you probably have to sue for breach of contract but I'm not at all sure about that. I suspect that if you just cut the padlock off it would be criminal damage so that's probably not the first thing to go doing without some sound advice.
well..............
You have a legal right of self help if you believe you have been wrongly prevented from use and enjoyment of you leased property. Its the same right you have, little known, of cutting off a private parking clamp if you have reason to believe you have been illegally clamped.
If you rent property you have a legal right to non-interference in the use of your leased/rented asset. Its exactly the same as the landlord changing the locks on your rented house, even though your rent is up to date and you have not broken any of the rules of your tenacy agreement. You have a legal right to bust the door down and enter.
i woudl write and ask them when they intend supplying you with a key. If they say they ernt going to, i would point out it amounts to illegal possession of your rented property. Depends how much you want to fall out with them about it.