[daveevans99]

i wasnt pulled over but think maybe an unmarked vehicle saw me speed (rang rover discovery in a rural area on a private plate) and then a marked car pulled over on the other side of the road about 1.5 miles ahead neither vehicle stopped or followed me what is the likelihood they are sending me a fine?

[olduser]

Depends how far over the speed limit you were.

If just a little over (said to be 10% but I would not bank on that) but driving sensibly probably no action will be taken.
Beyond that you will have to wait and see.
Most cars speedos are about accurate at 30MPH and indicate high above that, this may mean you were not going as fast as you thought.

[Santa]

They have 14 days to send a notice to the Registered Keeper asking who was driving.

[Beelzebub]

As above, they'll send a letter to the RK. They won't send anyone a fine. What they will send (to the driver, after he's identified) is the option of accepting a fixed penalty, possibly attending a course, or having the matter referred to court.

But it sounds unlikely that any of that will happen.