Santa:
I think it may have started when some firms became aware that some places gave a receipt for parking but that included a free meal etc. They saw this as cheating because the NO allowance is supposed to pay for the meal.I used to do it: pay £20 for parking overnight and get a ‘free’ meal, which would have cost £10 and claim back the £20.
That annoys the hell out of me does that.
A meal voucher is part of the contract of parking, it’s an inclusive perk for the driver, so has ■■■■ all to do with the firm.
The problem started when some places offered a choice of 2 parking tickets, one with one without, so the greedier firms (such as mine 
) picked up on it and insist on the driver handing in the non meal ticket.