Thanks everyone for the quick replies. I've owned Sula for 15 years now and pretty sure this repair wasn't done by the previous owner, so looks like it should be reasonably straight forward. Ten years ago we bought a new mainsail with small vertical battens from Deme Voils. Although through great care, we have had very few jams over these years, one does have to be quite disciplined in the manner one furls and unfurls compared to the non battened sail. Despite that we won't be going back to no battens at the next sail renewal.
Given her age and the huge amount of use our boat gets, a failure like this should probably have happened a lot earlier!