Thanks Tom, much appreciated.
I found two fuses in the starter relay housing - are those the ones you were thinking of?
Before I checked the fuses, I switched the bike on this morning in the over-optimistic hope that it might have miraculously sorted itself out overnight, but got the same indication. However, after about 20 seconds, the fuel pump started running, and the flashing bar disappeared. It starts & runs no problem now.
I have absolutely no idea what caused it or why it decided to sort itself out, so I can only think that its "age"! The bike is a 2013 one and has done about 55,000 miles in all weathers. Its behaved fine til now (that's why I buy Hondas!) and not had an electrical glitch in the 40,000 miles that I've ridden it.
Its due a service, so I'll ask the workshop to have a look to see if they can suss-out what might have caused it. I'll also spend a bit of time cleaning all the electrical earth-points, because that's helped with strange problems on other bikes I've had.
Cheers,
Jon