Gold standard in pedal bearings

Which brand / manufacturer produce the absolute top end sealed pedal bearings? I would also prefer to source from UK manufacturer.

Top-end and sealed don't combine. Which bearings fit your pedal depends, of course, on the pedal model. Since I assume you have cartridge bearings I'll talk about them-- with cup and cone you just purchase good quality balls from the same lot. Highest performance are typically shielded-- or even fully unsealed. The "Gold Standard" are high grade ceramics-- cheap, inexpensive ceramic cartridges tend to be inferior to similarly priced steel bearings-- but they are also quite expensive and not really of use beyond placebo. Speedplay uses 686 (13x6x5mm) outer and 137 inner (13x7x4mm). These are industrial products and best purchased from an industrial bearing supply-- where the bicycle companies also source them. SKF (Swedish) and EZO (Japanese) are quite well known and established makers but there are a number of other suppliers such as Schaeffler Group (FAG and INA) in Germany that also produce extremely high quality and well regarded bearings.