I overheard a conversation last weekend at the Kootenay Raid that most all Triumph engine cases are (and have been) manufactured in Asia for quite awhile now. According to the conversation it is mainly due to air quality standards allowed in Asia versus UK. Cases are shipped and the final machining done in the UK.

Then again it could all be conversation

"It's not what I say that's important, it's what you hear" Red Auerbach