Is there a number you can call to report them for booting/towing?
Probably not. All parking areas seem to be managed by the lowest bidding private firms these days. They don't have towing vehicles because employing somebody on a zero hours contract with a book of parking fine tickets is so much cheaper.
I think this also has a bearing on last year's Government cull of valid Blue Card holders. Every disabled Blue Card holder costs us money by getting free parking, dontcha know, so if we tell the Govt its costing them money the dozy sods will believe us and put a stop to it.
Biting the hand that feeds IT
