Thanks for that. From memory and my notes I believe that the majority of my shots were between 1/250 and 1/1000 for sure (it was pretty sunny).
The one full frame on the roll was definitely shot at 1/60 as the light had gone by the time I'd taken it.
I'm glad you suggested that as a plan because it's something I'd presumed I'd need to do. I'll take a test roll out with me tomorrow to test out.
My only confusion is that my previous rolls had worked (for the most part) fine, so it seems that potentially it has only recently become an issue.