What are the requirements for obtaining a Non-Immigrant B Visa in Thailand if I've lost my previous work permit?

Hi, I have a bit of a situation pertaining to granting a Non- Immigrant B Visa. I have worked in Thailand in the past and held a work permit. Now I am wanting to come back- looking at what I need to submit for a non-b these days I see that they need a copy of my old work permit. Alas, I do not have this as I gave it back to my old employer. New employer is asking for it, but it would seem that the old employer cannot help with this. I am trying to get the visa in London before I travel. Would it be easier to get the visa in Laos? I am worried about losing out in a good opportunity because of this at the moment.