VAT
I think this largely depends on who your cliental is.
Broadly, the pilots who shop around will be ones who have to self finance their medicals i.e students, private pilots etc
For employed commercial pilots their medicals are usually paid by the company so they will just reclaim the VAT no big deal as such.
If a majority of your clients fall into the first bracket then it would have an effect. If your clients fall into the second bracket, then I don’t think it will have too much of an effect.
Who knows whether HMRC will charge VAT on seafarers medicals and if they do how much money will it generate, I personally think not a lot.