I've pleaded not guilty as I don't think I was going the speed alleged.
The alleged offence is exceeding the prescribed limit (Not a specific speed). By pleading not guilty you are saying you did not exceed 50mph and would go to trial if maintained.
They claim that I was travelling at 90mph in a 50mph zone and provided dashcam as their evidence. In this dashcam or any of the evidence provided, you can't see my vehicle clearly or the VRM. The vehicle was stopped by uniformed officers in an unmarked car. The statement the officer has written, doesn't reflect the evidence they've provided either. I can accept that I was likely going over the 50mph zone as it was a dual carriage way that I thought was a 70mph zone but I don't believe I was going 90mph.
From the footage posted the Police were doing well in excess of 90mph (and the car being pursued did not get any closer).
As the officer says in the video, they're playing catch up, so I don't think the speed he's travelling at can be used as the speed I'm going?
It's quite normal. As long as they can sufficiently connect the dots (i.e. it was you and your car being pursued) then a conviction is extremely likely.
What's the likely outcome based on the evidence?
The excess sets the sentence. For a 50mph limit then the highest band (C) starts at 76mph where 6 points is likely or a short ban (up to 2 months). A fine of around 150% of weekly relevant earnings. (33% discount if pleading guilty at earliest opportunity) Surcharge of 40% of the fine and costs (Likely to exceed £600 if taken to trial).
However, 90mph could well be considered grossly in excess and the ban could be longer etc.
The alternative is a Newton Hearing (this requires a guilty plea). That is you admit to exceeding the limit but you do not agree with the excess. (Although looking at the footage I think 90mph is generous)
I think you should consider professional advice, especially if you want to maintain a not guilty plea.