Well when the letter arrives dave will be talking to a solicitor, I think its got to help rather than dave trying to fumble through the legalities.
Don't take the following the wrong way as I am only trying to offer advice;
I think Dave may need a reality check.
It is alleged that he was travelling at 110 mph on the M1.
It's 3am in the morning and there is no other traffic on the road except for a Police car which has been following Dave for 0.75 of a mile.
I appreciate Dave didn't realise it was a Police car but if I was exceeding the speed limit (which Dave accepts) on an open stretch of m/way and I could see headlights behind which were matching my speed, I would want to know what they were doing.
I would be slowing down to see if the headlights matched my speed or whether they continued to overtake me. If they slowed down, that alone should indicate to Dave that perhaps all is not well.
It would appear to me that Dave didn't notice the headlights behind. To conduct a 'following check' your talking of a distance of roughly 300 / 400 yards, so it's not as though Dave shouldn't have noticed the headlights on an open stretch of m/way with no other traffic.
Dave clearly wasn't paying enough attention to his surroundings.
Dave excepts speeding but is alleging a speedometer fault.
A cheap way to test his speedo would be to drive back onto the M1 and time himself between two SOS boxes when travelling at 70 mph. They are 1 mile apart (not calibrated). He will then be able to work out a true speedo reading and it should give him an indication as to whether his is faulty. Bear in mind it will be + / - several mph as most speedos are.
Dave can then decide whether he wants to go to the expense of having his speedo checked at 110 mph.
Dave needs to put his hand on heart and ask himself whether he was exceeding the 100 mph as most experienced drivers can tell without looking at their speedo.
Be careful about seeking legal advise from solicitors as very few are experienced in dealing with speeding offences and will charge Dave a fortune for saying a few lines in court which in most cases still get the same result ie. fine and a disq for a period of 28 days (example).
What goes in Daves favour is the fact that there was no other vehicles on the road (except the obvious) at the time of the alleged offence, weather and road conditions were presumably very good, nobody was put in any danger as a result of Daves speed. Speed alone is not dangerous other factors need to come into play.
If Dave is faced with a short ban don't forget to tell him to notify his insurance company as they may refuse to pay out other than 3rd party if he needs to claim b4 his renewal.
Plus if he fails to notify them when his renewal is due he may be guilty of making a false declaration to obtain insurance which will invalidate his insurance.
As I said in the beginning only try to help.