Good news - took the car in to be checked yesterday to be told there's nothing wrong with it and they didn't charge me for looking.
Bad news - the orange light is back on this morning, just as I was very nearly at work. I had the windows down to check if there were any noises - nothing. It's driving OK. After a natter with the doctor at work, he was wondering whether it's come on to indicate it's ready for a service (which is booked for 8 April).
ETA I've now knackered my computer. An engineer is coming on Saturday. It's hell being without a computer at home.
ETA just googled vauxhall corsa dashboard lights: it's to do with emission control. If I can get it through to 8 April without it flashing yellow, I might chance it. Why they didn't pick it up yesterday is beyond me, it was a vauxhall garage I took it to.!!
Yet another ETA. Just spoken to a very nice man at Vauxhall Bedford and we've decided I'll monitor the situation for the moment, keeping fingers crossed that the car will make it to 8 April. I said about it being the emission and he said he very much doubted it, the light that came on could mean anything.