Basically yes, the developmemt story of the original Astra is here: http://vauxpedianet.uk2sitebuilder.com/vauxhall-t80---astra-mk1-a and you can see from that that UK efforts were focussed on a restyling attempt that didn't make production. The Astra was probably the first major Vauxhall not to be restyled for the UK market (if you read the article the design studio was switched to commercials design after that), and wasn't even built here for the first two years of sales. UK input probably regressed from there, bear in mind that later cars and platforms had input from US/Japan/Korea/Holden/god knows who and where else.

Ford did a lot more engineering in the UK than GM, and still do, and there are Fords that probably should be Origin UK more than Vauxhalls. (The Orion, for example, was initiated by Ford UK as they were concerned Cortina buyers wouldn't buy the Sierra due to the hatchback bodystyle).

Vauxhalls default to origin UK and even where people change the origin to D some people think that everything with a Vauxhall badge is built in the UK, rather than a more flexible approach where UK-built Opels are exported whilst D and B built Vauxhalls are imported, hence our listings are so inconsistent.