Punch out of few web searches (ex: Carlton sun cycles workshop) and you'll find that TI acquired the Sun Cycles name along with other brand names prior to acquiring Raleigh. It appears that, after acquiring Raleigh, they moved Sun to the Carlton Worksop location and Sun's were produced there into the early '80's. A Carlton made Sun Cresta may not be unusual in the UK. I'll bet few were sold in the US.

BTW just in case you don't know - Worksop is a small town just outside Nottingham, where Raleigh was HQ'd. That is the right spelling vs "Workshop". Carlton's plant was located there for many years during its TI Raleigh era.