Your flight will be perfectly legal. You are not being paid for flying, but are being paid in your regular job for the time you spend en route to a meeting. "Motor mileage" equivalent is expressly covered and allowed by art 130 ANO. You can claim direct costs from your employer, which would otherwise pay your train fare or motoring costs. See the CAA's summary, linked to from the "remuneration" thread, although it sounds from your post as though you already have a good understanding of the rules. Have a good trip.