Although a copper, I work in another area of policing and haven’t dealt with a traffic matter for over 15 years. However this is what I think – you would be wise to research it yourself though 😀
It seems you’ve been lucky (if that’s an appropriate term). Had you been clocked at 76mph – the guidelines (under ‘Speed Enforcement’ in the below link) suggest you ought to receive a summons to court for a stiffer sanction than can be imposed by the Fixed Penalty Scheme.
http://www.cps.gov.uk/legal/p_to_r/road_traffic_offences_guidance_on_fixed_penalty_notices/
From the circumstances you describe, you are eligible to be dealt with by way of the FPS. If you wish to plead not guilty your case will be heard in court.
The Speed Awareness Courses are aimed at those caught speeding just above the limit and will only be open to people caught breaking the speed limit by 10% + 9mph or less – so, not you.
Please drive more responsibly in the future – thanks.