Thanks for replying. Sorry I've not managed to get back to you till now.
It happens mostly when I'm typing in an URL or subject heading in the browser.
I don't actively have anything running in the background, although there'll be automatic processes going on, I suppose.
I did try a reset, but icloud automatically downloaded everything back in, so that may have put back any problem there was?
I'm not really knowledgeable about the ipad (or computing in general!) so I may be missing something obvious.