I don't think I've ever been told anything explicitly, altho when the mw discharged me she said 'see you in 2 years', a bit like you, Becky!
C's 2 now, and we've got our first pre-conception appointment in a fortnight, aiming for a gap of not less than 3 years. Lots of reasons - my diabetes was really hard work for the first year after his birth, and I'm now feeling more comfortable that my hba1c should be close to where I'd want it for a pregnancy. I also had an emergency section with C, and would be planning an elective next time. We've not got family close enough / old enough (my parents both work fulltime!) to help a great deal, so we felt that C needed to be independent enough for it to be vaguely manageable.
Saying that, I think a second/third is hard regardless of the gap, it's just that diabetes gives you another thing to consider.
Again, I've never been explicitly told how long between pregnancies from a c-section point of view, but I've heard several other people say 12months.