Who is the middlesex insurance company? The Middlesex Insurance Company is a wholly owned subsidiary of the Sentry Insurance Group.Who are middx glass? Email: [email protected] Established in Upper Square, Old Isleworth, West London in the 1970s as glass merchants and glazing contractors specialising in the restoration and manufacture of traditional leaded light windows. Suppliers of 4mm 'Fluted' glass, a direct replacement for Pilkington Narrow Reeded.Can we help with double glazing repairs? Whether you need new windows and doors, or glazing “Window Doctor” repair services, we can help you. We specialise in offering cost effective, reliable glazing repairs services. Our proprietor, Kelly Dawett, has a background in engineering and can find a fix to any double glazing problem.