Finally got round to having new tyres fitted; just as well, as the rear off-side was in a bad way. The tread was good (very good in fact) but the inner wall had almost a 100% circumferential crack in the outer skin.
I opted for Bridgestone Potenza RE050 tyres, which I ordered from and arranged fitting through Black Circles. As of writing, one day later, they certainly make a huge difference. Lovely, smooth, precise feeling is restored....well almost.