Just to muddy the waters a little more...
Something I've wondered about in the past, is as follows:
I, as a PPL, hire a helicopter to fly myself to a business engagement. For simplicity, let's say it's just me in the craft. I'm hiring from a 3rd party, completely unrelated to my employer or myself (beyond being someone I self-fly hire helicopters from). I fly myself to the meeting and back again, paying the hire company £X for the flight time. I then go back to my employer and claim the £X I've paid as travel expenses (assume I have a massively generous employer).
Is this a violation of my license? You could argue that my employer is paying for my flying time, so under the 'valuable consideration' test, I'm getting some valuable free hours. On the other hand, I'm taking responsibility for paying for the flight time; there is a reasonable expection that I'll be reimbursed further down the line, but presumably no guarantee. Also, my employer isn't paying me specifically to fly; they're simply reimbursing me what I spent getting from A to B.
Obviously this is completely theoretical, as I can't see any employer agreeing to pay for basically the most expensive means of transport when there are definately going to be (much) cheaper options. I'm just interested as to how the situation would fit into the private / commercial structure.