Some Questions Regarding Certification Of Stamp Collection In UK

What are the stamps are you talking about? Are they very valuble. Why not post a scan of one or two to let us get some idea. Without some idea of what and why you are planning this is is difficult to advise.

Anthraquinone
I had sent some other topic before as the below link will take you there, it is just a few quick samples and I have got some other,

https://goscf.com/t/75677

My experience (such as it is) is that much like the most comprehensive catalogs for a nation are usually published by that nation (Yvert or Maury for France, Scott for USA, Michel, Sakura, etc) so the most reliable evaluations are done the same way. I would never [i]rule out[/] buying an American stamp with a German or French of British certificate, but all other things being equal, I'd lean towards the American one.

I don't have evidence for this at all of course, and no doubt there's a collector in Singapore who knows more about Mexican stamps than 1/2 of MEPSI for example... my statement above is just my collector prejudice I guess, but probably shared by a lot of people.