I wouldn't know, spudsey - it's been a long time since I've been in a "business oriented busy working pro commercial bands earning comfortably over a certain threshold"! But when I was, all sorts of things were tax-deductible - petrol for gigs and rehearsals, car servicing, equipment maintenance (no PAT testing in those days, though), dress cleaning, strings, telephone calls, etc.

If you go to play at a gig for no fee - unless you're whisked there by an ethereal transporter and all your gear is provided - then you're playing at a loss in any case!

All I'm saying is that you have a choice - if you don't want the costs and inconvenience of PAT tests, then don't incur them by all means - and choose venues which don't ask for such things. :-)