I plan to spend about 3-4 months pa in Thailand during the colder months of N. Europe once I decide to retire from my full time job, by which time I'll be pushing 67. Good all round health currently but that could change so insurance is a must for those periods I am in Thailand. Can anyone recommend a reputable Thai company, or even Brit company? Maybe it would be better to get an annual one for wider travel, including in Europe(?). Not looking for the cheapest necessarily. Would appreciate advice.

If it was me I would buy a long stay travel insurance policy for the 3/4 month period which will cover you for all of that time in Thailand plus flights etc. Last time I looked most standard annual travel insurance policies would only give you 30 days per trip or similar.

Googling long stay insurance policies should bring up the usual suspects including World Wide Insure, World Nomads etc depending on what country you are in. No idea re age and you would of course need to check all the benefits carefully.

May be worth doing a search in the Insurance forum as this has been discussed before and for Thai based insurance you could check with AA Insure - broker based in Thailand http://www.aainsure.net/