Exactly where has the belly moved up? Between the the bridge and the fretboard or, more likely, between the bridge and the bottom of the guitar? If it is the latter, it's not normally a big problem (even normal on some guitars) unless it has bellied excessively. Let me know and I'll try to suggest a figure for a general overhaul/check/setup that should be reasonable in the UK. Where are you based (if you are the Jon I've met then I already know!), I might even be able to suggest someone if you don't already have your own repairman.
As it's a Fylde Falstaff it's well worth getting into top playing condition as they're a smashing guitar!