I am also based in the UK, and I use SGS for my ISO9001 & IATF16949 Certifications, and I also used SGS for 8 years in my previous company for ISO9001 & ISO14001.
My current company has been with SGS for 15+ years, and my next audit will be my final surveillance audit in a 3 year cycle.
After my experiences over the last 6 years, I will be looking to use anyone other than SGS for the next re-certification audit. Over the last 6 years their costs have continued to increase at an unjustifiable rate while the quality of their auditors has severely diminished, and communication with their account managers is poor and at best.
You may be dealing with a completely different group of people on the medical devices side, so my experience may be of no relevance at all.
I have been a loyal customer of SGS for over 2 decades, but this will end next year :-(