>>>I have just got the paper work through
Which paperwork is it? An 'ordinary' speeding offence normally results in a 'Notice of Intended Prosecution' being sent out, which provides the option to pay a £60 penalty and have 3 points added to your licence. However driving at well over the speed limit (such as at 95mph) might result in the option to pay a fixed penalty being withdrawn; in that case a court summons would be issued. (I've seen a couple of cases recently, here in Suffolk, where the magistrates imposed fines of £800, plus costs, on people convicted of driving at high speeds, together with a short driving ban).
Further, failure to produce your driving documents at a police station, within the prescribed time, is also an offence. Are you being prosecuted for that as well?
As others have said, the was no obligation on the police to caution you.
The chances of the police even pointing a radar gun at a car driving behind a lorry would be almost zero. (The lorry would be subject to a lower speed limit than the car so, if any speeding was occurring at that point, they would be far more interested in the lorry driver than you. It seems far more likely that you were speeding earlier on and that the police had only just caught up with you.
Further, while I certainly don't have any great confidence in either the honesty or the intelligence of many police officers, any copper can tell the difference (without any technological aid) between 95mph and the maximum 56mph that most lorries can travel at. If a radar gun was clearly registering about 30mph above the true speed of a vehicle, he'd get the gun checked out rather than continue to use it.
If you've received a 'Notice of Intended Prosecution', pay the £60 and consider yourself lucky. If you've received a summons, you'll have to appear in court anyway where you could, if you so wished, tell the magistrates what you've told us. But don't be surprised when they find you guilty anyway and impose a higher penalty than if you'd simply pleaded guilty.
Chris