Before talking about a 'decent FIS', perhaps it's worth understanding just what a FIS amounts to...? There's still a Safety Sense leaflet about types of service...
Aha! Obtain a FIS from the likes of Farnborough and see how it compares to the 'same' service from London Information. That's what I mean by a "decent FIS"...one that comes with a squawk. The contractual obligation is no different from the official definition of a FIS so I assume this is why ATC prefer FIS to RIS.