Firstly, I should disclose that I am the EU261/2004 compliance official for my airline and hence I spend most of my time figuring out the loopholes to benefit the other side of the coin.
I was also wondering where you find out what a specific regulatory body does decide that 5 Euros/£5 is appropriate. Do these regulatory bodies benefit from subsidised canteens and hence they regard this as a realistic cost of a "meal"?
The few times that one of our passengers has complained to the AUC (Air Transport Users Council - the body responsible for enforcement in the UK) about the inadequacy of the £5 voucher, we have invariably received a letter asking us to justify how it constitutes "meals and refreshments in reasonable relation to waiting time". What we do is respond with a sample list of possible meal and refreshment options that fit within that budget, and the AUC has always been satisfied.
You'd be surprised how far £5 can get you at Gatwick actually. Most passengers use the vouchers at McDonald's or Burger King and it will buy you virtually any Combo meal there, plus a dessert item in some cases too. For the more finnicky eaters, you can get a salad or personal pizza from Pizza Express, a premium sandwich at M&S Just Food or a Healthy Meal Combo from Boots - all easily within the budget. It isn't Michelin star dining, but it's not intended to be - it's usually better quality than the stuff we serve you on board though!
Most of the complaints received however deal with the issue of what constitutes an "overnight" delay that requires hotel rooms to be provided. For example, a flight delayed from an originally scheduled 2300 departure to a 0500 departure would seem to meet the definition of "overnight" to a normal person. Unfortunately, in reality an 0500 departure means that passengers have to start checking in for the flight around 0200 and hence have to leave hotels around 0100. There is very little point sending passengers to a hotel then for what is essentially no more than an hour there - especially as some will invariably fall asleep and miss the check-in deadline and either be left behind or wind up delaying the flight further. Our unpublished rule-of-thumb is "a delay of more than 9 hours, of which at least one-third or 6 hours (whichever is greater) falls between the period of 2200 to 0600". We have always been able to justify this on the basis of the proviso that "provision of the care would itself cause further delay", but it is a no-win situation for the passenger in cases like that as they feel rightly aggrieved.