Just a note to check this one with an accountant.
Many years back when I was self employed for things that were used for both business and personal use (Eg my car), I had to declare a % Business use, and could then claim that % - so if my car was £5k, and I claimed 50% business use, then in effect I could claim £2500 for the car against tax.
My accountant knew the various % figures for a range of things that HMRC would accept, and advised accordingly.
It may be that for a photography business, they'll accept 100% for a camera, lenses, etc. and not care that you actually are using it 75% business, 25% personal (for example), but it you have a friendly accountant it's worth checking.