Oh god don’t pay anything until it is cleaned & dry & all removed! Not one penny!
If he comes to your house tomorrow, cleans carpet as best he can & sorts out dodgy patches in paint, & then demands payment, tell him you need to WAIT until paint and carpet are dry to assess whether stains removed & paint now ok (this is true). This will get him out of the house.
If (unlikely) the problems are completely dealt with, when paint & carpet are dry, pay him less the £100 deduction.
If either carpet or paint (or both) are not completely sorted out, when dry, message him to say you have given him a chance to rectify, he’s failed, and you now need to get professionals in - and that he will be responsible for cost.
Deduct the cost of any remedial paint work from what is owed, PLUS deduct the cost of a professional carpet clean and (if necessary) the new carpets.
If you have to get new carpets, your total cost (carpet cleaner, new carpets, remedial paint work) will exceed his invoice. Then you can either make a claim against him in the small claims court, or wait for him to make a claim in the small claims court against you for his invoice, and then make a counter claim against him.
This man is a cowboy & clearly exploiting you because you’re on your own. What a complete shit. No professional would do that.