My visa is about to run out - 4 weeks left. I plan to head back to Thailand going through ASQ etc again.

 

Do i need to go through the whole rigramole of the visa application again, or can they just renew it automatically?

If your current visa expires while you are outside Thailand you will need to apply for a new visa.

Do you have a valid visa issued by an embassy or a extension of stay issued by immigration. What is it based upon?

I don't think 4 weeks will be enough time to apply for a certificate of entry if you qualify for one.

You cannot renew a visa, only an extension of stay.

 

Who are "they" that can "renew it automatically" ?

 

Either way, if you can get a Certificate of Entry from the RTE in London, based on what you have, you need to get back to Thailand before that expires.