Well they have 14 days to issue a notice of intended prosecution (the fancy way of saying send a 'we caught ya' letter), if it arrives after that then they can't prosecute you regardless.
Not all cameras flash. It may have been off, it may have been faulty, neither of these are guaranteed. Sometimes they're off at 5 in the afternoon, sometimes they're on at 3 in the morning.
Did you notice the white lines? If they're weren't any then you may be able to fight it by arguing a miscalibration and therefore a wrongful reading which is why most cameras have them, but fighting it is expensive and worsens the penalty.
Depending on the motorway it might have been an average speed checker camera so may have just registered your plate not your actual speed.
Contrary to advice you can be prosecuted for 1mph over if the police are feeling like particular d!cks (well the CPS) - they just usually don't bother. Whilst your speedo is set usually a few mph above actual speed it depends on the make of the car, and a load of other variables ie a loose pin might mean its showing you a lower speed than you're doing. Most cameras are calibrated to only gun about 10% over but this can be changed at any point. Plenty of convictions for 75mph in a 70 zone about.
For a minor speeding offence you shouldn't lose your license, its 3 points and a few hundred quid or if the judge is feeling generous a speed awareness course. Just make sure you have a part time job and save hard because your insurance is gonna skyrocket if you get charged. Honestly why on earth are you leadfooting just after passing your test? I'm not convinced about your instructor if you don't notice 10mph over for long enough to pass a speed camera - that's basic driving. It's also dangerous, if you hit water or oil you'd spin out and wreck unless you have an excellent innate driving talent, new drivers rarely know how to counteract high speed incidents, its one of the failings of the test.