There are many health problems that can cause a rabbit to stop eating. Basically anything that causes a rabbit pain can cause them to stop eating. It could be anything from a cecal impaction, urinary or kidney problem, heart problems, to dental issues(which can't be completely ruled out unless the dental check was done under GA as a conscious exam isn't as thorough). You may need to have xrays and blood tests done at this point, along with a thorough dental exam under GA.
A rabbit
not eating is a rabbit in pain.
That is the evidence of a rabbit being in pain. Just my opinion, but any vet that doesn't prescribe pain relief for a rabbit not eating(and with no evidence of kidney issues), likely isn't a rabbit savvy vet. Rabbit savvy vets know the importance of adequate pain relief in a rabbits recovery from illness and to help get them eating again. If your vet didn't prescribe at least some metacam/meloxicam for pain relief, it's likely the vet isn't a rabbit savvy one.
http://www.veterinarypartner.com/Content.plx?A=500
Am I guessing right that you are in the UK? You have several very good rabbit specialists in your country. If you would like to post your general area, I might know of one near your location. Seeing a rabbit specialist can make a big difference in a rabbit getting the appropriate diagnosis and treatment.