Not sure about an 02 plate GC, but have finally got a spare fob for my 97 TJ sorted...
It seems that when Chrysler imported the Jeeps, they didn't have immobilisers fitted. Chrysler UK therefore subcontracted the job to a lot called May & Scofield. Since then, these people have stopped supplying Chrysler, therefore offer limited tech support to the dealers (what few there are left!)
I also gather that re-coding the fobs can be a bit hit and miss, with some reports of even complete immobilisation after re-programming!
I bought a second hand fob off of eBay for around £10
May and Scofield were helpful for me, and I found a Jeep garage in Cambridge that were happy to give it a go (Peterborough and Nottingham didn't want to know!) and now all works fine...
Got a key cut at Timpsons and job done...
Like I say, may be different for later models, but that's my 10 pence worth...