I'm not as sure about the laws in the UK, but I'm a designer working in the US and I've often had to sign a "Work for Hire" agreement â" essentially stating that my client/employer owns the rights to my work once I've been fully paid.

http://en.wikipedia.org/wiki/Work_for_hire

I've always seen this in reference to the 1976 copyright act in the US, so the timing's a little funny with a movie from 1977...so who knows how it was defined. But it's worth keeping in mind.