Apologies for the paint problem.
This is an issue that far too many people have with the solid red Mercedes paint, as @MuffinClaw pointed out. Surprisingly, the micro-blistering doesn't impact the vast majority of automobiles, but when it does, it seems to harm every single metal panel.
If I were in your shoes, I'd try to get Mercedes-Benz to pay for a complete bare metal respray first. If they disagree, you'll have to make up your own mind about whether or not to accept their offer. I would next file a complaint with the Motor Ombudsman and hope for a positive resolution.
The legal process is expected to be lengthy and expensive, as Mercedes-Benz UK is known for fiercely fighting accusations. I hope that won't be the case.
Wishing you the best of success with your claim. Please keep us updated on its progress.