FYI.
Just so as you are aware, there is NO POSTAL service at ANY of the Thai consulates in the UK. It is strictly an attend only service at UK consulates now.
Some also need an appointment to attend and can have odd closure days. I suggest contacting them in advance before you intend to travel.
One more point, you CANNOT use the London Thai Embassy online only application service to apply online then attempt to collect your visas at any UK consulate. If you apply online, you then have to use London by visiting or posting your documents to them or any Embassy taking part in the online scheme you have chosen to collect your visa from.
At this time, only London, Paris and Beijing plus consulates in China are included.
List of UK consulates with contact details in the link below
[members only]