Well, it doesn't seem to be the 'end tag errors'. Tried fixing those, but they didn't solve the problem.
I've fixed it by changing how I embed the copy and images into the pages and changing to a 'Joomdalf' component for the accordions (rather than Widgetkit). It looked to me like the problem was with having numerous YouTheme Widgetkit slideshows embedded in articles and using Joomdalf to create columns and adding translatable text into those columns, alongside the Widgetkit slideshows, then having Widgetkit accordions following those on the same page.
I made the Widgetkit slideshows modules rather than embedding in the article and removed any translatable text from them. These were the cause of the problem.
Then built the accordians within the article using JoomDalf.
Anyway, all fixed.