Nakamichi is the obvious choice - B&W do a great job repairing or in my case converting a CR-7A (US model) to UK configuration.
Revox, terrific machines although repairs can be costly, Brian Reeves in the greater Manchester area is a top notch technician and former Revox employee.
I see the Walkman Pro gets a mention and so it should, an excellent component which belies it's lowly status when compared to the aforementioned. It is very good in record and playback mode. An Italian guru - dottor walkman - can do amazing things with these machines at a price of course.
Which leaves us with:
Tandberg; from many accounts the best and most difficult to obtain parts for.
Arcam; the Arcam Delta 100 is a UK made component (maybe using Denon or Sanyo parts) and got good reviews, tend to be rare though.
Pioneer; many of the forum members at
www.tapeheads.net use a CT-1250
Sony; the TC-KA7ES
Studer; the A710
T+A; German company who still or until recently manufactured cassette players.
and Aiwa, Denon, NEAL, Kyocera, Hitachi...