Thank you. That's what I suspected. We call them Holland lops here in the States, and that's the breed I raise. When dealing with dwarf rabbits, there is actually a dwarf gene involved. Each rabbit has 2 genes to determine size; it got one from each parent. WE'll call the gene for normal size 'N' and the gene for the small size 'D.' Dwarf rabbits that grow up to be healthy adults have one of each gene, so ND. If a rabbit gets the N gene from both parents, so it si NN, it will be larger, with a more pointed face, and longer ears. If it gets a D from each parent, so DD, it is in trouble. Such bunnies will be smaller than the others, and among show breeders are often referred to as 'peanuts.' Because of how genetics works, when breeding dwarf rabbits, about 1/4 will be DD. Most of them die within the first week after birth. Once in awhile, one lives to be 3 to 5 weeks, then the health problems associated with having the double D manifest, and they will die. It is especially sad then because they are at their very cutest. Your little bunny is most likely a DD, or peanut. That clicking sound you hear indicates a breathing difficulty, probably pneumonia. Because of all t he circumstances involved, it si highly unlikely that he will respond to any treatment, but if you wanted to do everything possible, you could take him to a vet. This link will take you to a list of UK rabbit vets:http://homepage.mac.com/mattocks/morfz/Vet_EU-UK.html
However, in all my years of rabbit breeding, I've never seen one of these little ones survive to adulthood. I'm so sorry to give you such unpleasant news, but I feel you deserve an honest answer. I feel bad for you, and wish I could give you a remedy, but I'm afraid there simply isn't one. If you have more questions about this, just let me know by clicking on REPLY. All you can do for this little one is let him know he is loved and keep him comfortable.