Those living all over the British Kingdom are big knitters and I wouldn't be surprised if sweaters on tv shows there were handknit. I have a friend who knits shawls and she lives in Edinburgh. She makes the most beautiful things you have ever seen.
There is a knitting blog that looks at movie sweaters and comes up with patterns that are close to the original. You might suggest the sweater from Lake House and see what happens. There are certainly lots of fans of the movie and the sweater.