Am I mental or do I have a hope in hell?
An interesting way to put it. Different countries have different requirements, so perhaps it is not an issue in the United States. Unfortunately, monocular vision north of the border is invalidating for a Category 1 medical. Unfortunately, you are a case study for why I consider it important for trainee pilots to obtain the highest level medical before pursuing flight training. It's better to "waste" 700 pounds to find out you cannot hold a Class 1 medical than waste tens of thousands hoping a Class 2 will be converted to a Class 1 later on.
With that said, I do know of pilots who have successfully challenged a medical before and were successful. Just understand that if you go down this route, it is possible the CAA would require you to jump through these hoops during every renewal, and any further decline in your vision would likely be cause for them to take the medical away. Alternatively, they could further change the medical rules one day and suddenly you find you are no longer restricted or restricted further. I don't think it's a great idea to proceed with your Class 1 knowing that you will fail, as other jurisdictions you may go to often ask if you have ever failed a medical, and you'll have to answer yes. Your better option would be to reach out to the CAA directly and ask to speak to their medical board. It may still cost a bit of money, but at least you don't have to admit that you've failed a medical in doing so.