I would be very surprised if any of the top kit, from all the respected manufacturers, is made here in the UK.
The only clothing, that i know is totally manufactured here in the Uk, is from Hilltrek, in Arboyne in Scotland.
They manufacture most of their clothing from Cotton Ventile, and i visited their premises a few years back, and you can see the manufacturing process for yourself.
Their clothing is very pricey, mostly because of the use of Ventile, and that its made here in the Uk.
Production costs here in the Uk, are incredibly high, which is mainly the reason for clothing being manufactured in the Far East.