Did the G techniq have any adverse effects on the clearcoat?
As mentioned above, all abrasive polishing will have an affect on the clearcoat, but unless something drastic happens it certainly won't be adverse.
The polishes mentioned above are all very filler heavy (with the exception of GTechniq P1). SRP is not abrasive in any way shape or form, it is a chemical paint cleaner with loads of fillers and IMO only really should be used after all 'polishing' has taken place to be used as a base for a LSP product. It may temporarily mask the scratch/swirls but it will not remove them. Paint Renovator is an abrasive polish but it's still filler heavy.
The only way to remove the scratches properly is to remove some of the clearcoat. As a general rule of thumb there is around 50-70 microns of clearcoat on top of the colour coat*, and even with wet-sanding a scratch from my bonnet, machine polishing back in 3 stages I only removed 6-7 microns. To remove this amount of clear, you need to introduce some heat into the paint and you can only really do that with a rotary machine polisher. Polishing by hand may give a reasonable result but it will take ages as by not introducing the heat that you can with a machine, the level of cut is massively reduced.
If you want to have a go, I'd suggest using a proper abrasive pure polish with no fillers such as Scholl S17+ (medium compound). IMHO (after lots of trialling in my early detailing hobby!) Megs Ultimate Compound or any Autoglym polishes just aren't up to the job.
*Paint finishes can vary from the factory and may be more or less depending on whether they have had any previous polishing. Only really safe way to check is with a paint depth gauge.
Sorry for the long post, just thought I'd shed some light on clearcoat thickness and information about polishes/filler heavy glazes.
Jon
