We found the person very rude when getting my wife's visa .we waited in a line with all the paperwork in order and because my wife's money to pay for the visa .she had to get out of her purse they sent us to the back of a line of 30 people . this is just my experience...
I think you might struggle because the Thai Embassy in London are so unfriendly and unhelpful and never answer the phone.they will probably say go back and do it in Thailand .but if you do .make sure you use a direct flight and clear it with the airline.my wife's passport only had 5 months on hers and needed to change but couldn't get on with the embassy so we flew direct with Thai airways ...
Medical insurance is ok if you're young and in perfect health but not easy to get when over 65 . health insurance is not mandatory for existing retires in Thailand yet . only if you apply for a retirement visa in your own country and if implemented on existing retires it will be a disastrous for old Farangs . this government needs to think good and hard about this .....