Do you love your pig? Do you want him to die? I'm assuming the answer is no, or you wouldn't be here asking for advice.
The fact that he isn't eating by himself AND is losing weight, means that you have a very serious situation on your hands. You cannot sit back and wait for something to fall into your hands.
Your options as I see it, are as follows:
1) Go to a recommended vet locally (one who is recommended for dental treatment) and nurse piggy at home. At this stage, you're looking at feeding and medicating throughout the day and night.
2) Get piggy up to Debbie in Northampton where he can be nursed by her, and see the Sanctuary's vet, who is widely regarded as THE man for guinea pig dental work
http://www.teasnorthampton.co.uk/ There is a large, national network of volunteers that make up The Piggy Bank. Between them, they've transported pigs the length and breadth of the UK, often saving lives. They give up their own time to do this out of their love for guinea pigs. If you wish to send piggy to Debbie, the Piggy Bank volunteers may be able to give up their day off work to help with transport. We do often ask for travel expenses (i.e. fuel) to be paid, as it's an entirely voluntary set up.
3) Deny your pig the medical treatment that it requires, thus failing to meet the RSPCAs guidelines and commiting a crime under the animal welfare act, the maximum sanctions being a £20,000 fine, a 6 month jail term, and a lifetime ban on keeping animals. "
Under the Animal Welfare Act 2006, the maximum penalties available for an offence of causing an animal unnecessary suffering are a fine of £20,000 or six months’ imprisonment, or both."
The decision is entirely yours.