I'm pretty sure I've been there (a previous partner's parents live in Truro). From what I recall the cornish ice-cream is similar to http://www.minghella.co.uk/Default.a..._ice_cream.jsp (which I prefer to Loseley's - Minghellas ice-cream is sold at the South Bank Centre BTW).

According to wikipedia, the main difference between frozen custard and high quality ice-cream is in the way it is frozen rather than the ingredients. This makes sense to me - it did seem quite different to what I'd had before. Wikipedia also says it was a huge food fad in the 1940s