I have been reading order 1188.
Interesting wording "direct costs of the flight otherwise payable by the pilot in command".
So if I am a PPL and I rent the airplane - OK let's say GBP200/hr a trip from A to B of 1 hour and I have a px so GBP100 to him and GBP100 to me. Splitting the direct cost (we'll forget about landing fees).
However if I am an owner/pilot things become more complicated. So my "direct cost" (my marginal cost?) is not so clear - if it said marginal cost I would have understood. Direct cost maybe no so clear - is it fuel, oil, cut of the cost of my 500 hour time limited mags, vac pump etc. Or is the direct cost the total annual cost of operating my airplane less the fixed costs (insurance, hangarage, registration etc etc) divided by the number of hours in the year. Each one can produce very different figures - now here is the wheeze - if I am doing the flight anyway does that change my direct costs.
With the FAA system it is clear - the cost for an owner pilot is marginal cost so fuel, oil, engine fund (subject to some provisos) and we have to have been going to the destination anyway (the common purpose).
Also is the cost the cost of taking someone somewhere under the EASA rules could also include the cost of coming back home without them?
All that said it does look to be legal in the UK - something which is very liberal compared to the US.