Contacted a chimney sweep who said he wasn't gas safe certified and I needed to contact a heating engineer first...the white bits are literally crumbling in my hands....not good! I've about given up with all the hassles getting tradesman out!
Could you try one of the fireplace shops/showrooms for a bit of advice? Am sure they'll have recommended tradesmen for installation/servicing. There are loads in the industrial estates around The Kingston bridge ( Tradeston) & Renfrew.