While I am a U.S. attorney, the U.K. and U.S. are essentially the same on these issue in practice: "reasonable wear and tear" is a classic issue of fact to be decided by the judge (unlike the U.S. there are never juries in U.K. landlord-tenant disputes) based upon the evidence presented to him and his or her good judgment if the case goes to court.
There won't be a lot of case law that is specific enough to provide guidance in your particular case (if any) because cases like these aren't worth appealing and creating case law on and because the law intentionally vests judges with great discretion on these issues and only intervenes in appellate decisions when a judge is deeply out of line. The legal definition of "reasonable wear and tear" is basically vacuous and don't provide much meaningful guidance.
I know you are joking, but no, do not set it on fire. You will find yourself incarcerated for arson, with a felony criminal record and a restitution judgment in the amount of the damages and a fine and court costs as well, and your credit record will be screwed and no one will rent to you ever again if they find out by doing a cursory background check. Your mum probably won't even invite you to Christmas dinner this year.
If they charge your security deposit and you don't think you owe it, you would have to sue them for a return of the part of your security deposit you don't owe, knowing that you face a risk of paying their legal fees if you lose, but will get your fees if you hire a lawyer and win (caveat: there are more nuances to fee shifting in the U.K. courts than I spell out here which are rather technical).
If they say you owe more than your security deposit and you don't pay, they can sue you for the balance, knowing that they face a risk of paying your legal fees if they lose, but will get their fees if they win.
In practice, it doesn't really make economic sense for either party to hire an attorney because the amount of the fees is so high relative to the amount of money at stake. The security deposit is 2-4 hours of legal time, and the amount claimed is maybe 7-14 hours of legal time, neither of which is sufficient to address the respective issues economically in a fully litigated hearing.
Short of going to court, you can provide them documentation and your video to show that you are right and to discourage them from docking your security deposit (in full, anyway) or suing you, ideally A.S.A.P. before they are too committed to taking legal action. You could also propose a compromise and see if you can get them to agree to it with neither party facing the risk of going to court.