Can I stop in London for a week before flying to Bangkok if I'm applying for a Thai visa from Canada?

As long as you have the correct visa for Thailand you have 90 days to use it doesn't matter where you fly from either.

The Thai Consulate in Vancouver is excellent they are very helpful and if you have any qustions thet will answer them PDQ. Perfect.

You cannot stay in Thailand permanently.

I just moved here from Canada. Just come on a 30 day and apply for your visa in Thailand. Much easier. I had mine 28 days after arriving

If it's the same as UK you have 3 months to enter Thailand to activate your visa,don't think it should make any difference what country you fly in from,

This is no problem at all, if you have the visa you can fly into Bangkok from anywhere. The main thing is that the visa and specifically the date is valid.

It might be. Some embassies have a strict requirement that you must show a plane ticket from where you are applying for a visa to Thailand. You could try uploading both your ticket to London and then your ticket from London to Thailand though.

You may need to get creative on how to upload it since the system usually only lets you upload one document.

If they're not happy with it they will email you. Then you can just look at getting a plane ticket from an onward travel ticket website