That’s the Latham I went to. Excellent quality birch plywood. When I bought it, the chap on the phone did say that they were having difficulty sourcing it. I still need another three or four sheets. Unbelievable how fast it gets used up.Lathams have a depot in Leeds that supplied me when I lived in Formby on Merseyside. The Birch ply was excellent. At present you may well have trouble sourcing it though, I know I could not get it about a month ago and resorted to Poplar for my 18mm, although I managed to get Birch in the 12mm, 9mm and 6mm sheets.
In late September they did supply me with 18mm at a cost of £88 + vat for S/BB grade.
Colin