ISTR some argument about a G/A handling monopoly being a violation of some EU ruling. Not sure you couldn't fight back on that, even now.
I gather that mandatory handling is illegal if there is just
one handling agent.
But this is moot in practice because what happens is that if you are running A Big Airport you invite bids for the franchise from Harrods Handling, Signature, and 1 or 2 others, and they all agree (under the table) their pricing to be similar.
The real issue is not in what these posh bizjet-service outfits charge (I don't think their well dressed and impeccably mannered gurls are on the NMW); it is that Mr Big Airport Manager (with an MBA from the Univ. of Upper Warlingham and wearing a well ironed yellow jacket everytime he leaves his office) has allowed this to happen in the first place, without making a provision for lighter GA to use the place
It is a rot which is setting in all over Europe.
The cause is probably in the continuing romantic view of aviation, where jets are seen as desirable and anything with a prop is not.
The dumb managers have no concept of marginal costing i.e. all the time the runway is unused, and since absolutely nobody working in traffic management is paid per movement, if you let a TB20 land there and get £25 off him, that is £25 you would not have made otherwise.
The cost of allowing that would be a zero-handling "GA entrance", suitably separated from the passenger jet apron. Might have to employ 1 person in there to collect the money, etc. A lot of airports do exactly that.
But most airport managers are too thick to see this and are happy to waste the place for the sake of seeing a number of jets each day and the runway sits empty 95% of the time while the ATCOs and their assistants and the fire crew and everybody else are costing them millions a year.