Hi Adam,
Thanks for responding so quickly.
Sadly I'm a victim of not following the rules, as I updated the main production server and didn't test first on one of the dev systems. Although I didn't state it, I'm intending to continue the investigation on a dev server, once I can restore service to the production box - yes it's my fault for being hasty on a Sunday night.
As it happens, the dashboard briefly reappeared this morning (one time only again), so I captured the HTML source that was generated and I also have a copy of the page source that generates a blank.
Sadly I'm still stuck with a production server that's generating blank pages - any advice on a safe regression path would be very much appreciated, as we're in the middle of an unrelated P1; it's been a bad start to the working week :-(
Thanks again
Darren