If your rabbit is not responding to treatment then your vet may advise you that it is kinder to the animal to have it put down. The vet will administer an injection which will send your rabbit gently off to a permanent sleep. It costs around £10 and is a service offered by all vets.
However your rabbit has passed from this world into the next, it is important that it is laid to rest in the appropriate way.
There are two ways to perform a proper rabbit burial:
Go to a vet for a cremation. This will cost around £7
You could bury it in the garden, perhaps under a favourite tree or bush, however be advised that Government Regulations forbid this.