In reply to Indy:
The gallery have said that they don't think any photo should sell for less than £200, and that in general photos are undervalued. They have only just opened, but have clients who are willing to pay that (and more) for pictures. I'll know prices more accurately once I've sorted out how much printing/framing will cost.
Putting it through the business is the obvious route, I just wasn't sure if HMRC would question it, particularly if I don't sell any and end up with 6 pictures as business assets in a company that (typically) wouldn't need them. I guess if they all sell and costs are cancelled/exceeded by income it won't be a problem.