//The Police would not be sent in droves to an empty carpark at a Reservoir would they? They were already there when the girls arrived.//
It’s probably a popular place for walking and the Derbyshire Constabulary (who have "previous" in this area) has taken it on itself to enforce their mis-interpretation of a law that is quite clear. You can leave home if you have a reasonable excuse. One of those quoted is to take exercise. No restrictions are placed on that. As far as I could see from the footage, there were no other people around (apart from the police).
//Surely they could have walked five miles if they were so desperate to exercise.//
If you are suggesting that it is the driving that caused the problems, why is that? The idea of the restrictions is to prevent spread. What presents more risk, driving five miles in car or walking five miles outside?
This issue is a mess. I understand the two ladies will contest their fixed penalties and I wish them luck. If the government wants to stop people straying too far from home, or to prevent them walking in popular areas they need to legislate properly and not allow this “back of a fag packet” guidance to allow the police to act unlawfully.