Speeding fine(s)

i don't know, but i would think having broken the speed limit cannot be a defence against breaking the speed limit again.

This is from 2015 but seems to describe your situation :

the Court has discretion to impose only the one set of points for two or more offences. Whether or not offences will be treated as committed on the same occasion is a matter of fact for the Court to decide. They need not have been committed simultaneously, but they must be linked in some way.

For example this month we represented a driver who had been caught twice by different speed cameras, on the A4 West Cromwell Road in West London. The cameras were only half a mile apart and there were only four minutes between the two offences. If our client had simply accepted the two Fixed Penalties the police issued, she would have ended up with six points. Instead, despite police opposition, we were able to persuade the Court to impose only one set of three points.

www.richardsilver.co.uk/news/caught-speeding-twice-or-more-on-the-same-journey-how-many-penalty-points-will-you-get/

In theory, if you were caught speeding by two different speed cameras, you could be fined and have penalty points imposed for both offences - but in practice, if it can be argued that if they were committed during the one journey, the court can treat it as one incident. It's down to the discretion of the court - or up to your lawyer to argue that it should be treated as one incident.

Look it up - it’s complicated, but if you get legal advice, there’s a chance you might be able to argue that both times you were caught ‘on the same mission’ and the court might treat it as one offence.

However, signs advising of speed limits would have been visible - to say you didn’t see them could indicate driving without paying attention.

I think you should just accept that you were in the wrong, committed 2 offences and have been penalized - you’ll also have to advise your insurance company of the points.

To be fined at 71mph there must have been a lower restriction eg 60, there has always been a few mph tolerance. On many motorways the average speed for cars is well over 80, the only time many cars obey the limit is when there is an average speed control, which are becoming more common, not just road works.