I believe Gary generally uses a Gibson Les Paul through an Ibanez Tube screamer into a Marshall Valve head with the input gain turned up high, drive about halfway, output master high, which will create a natural compression and harmonic, a tad of Spring Reverb, and finally into a 4 x 12 cab (or cabs). In order to get reasonably close to his sound try medium overdrive / Distortion + Compressor + Spring Reverb into Valve simulated (preferably Plexi sound) amp and the speaker cab set to British 4 x 12. This should give you the basic building blocks. Take it easy on the distortion as Gary's sound is relatively clean but go for max sustain as clean as possible. Also be patient with the compression as it is a very subtle sound but will help the sustain and the valve style harmonics. I saw Gary before Christmas at the Fender Stratocaster 50th Anniversary concert in London and he was using a standard Strat and achieved his Bluesy tone so the Gibson Les Paul Humbuckers can be substituted with Strat single coils ! Good luck.