If you are unlucky enough to get two Notices of Intent to Prosecute (NIPs) timed within a few minutes of each other you shouldn't be charged twice.
Assuming that you are willing to accept the first offence and pay £60 and take three points then you will almost certainly succeed in getting off the second.
Section 28 (2) of the Road Traffic Offenders Act 1988 deals with multiple offences committed at or around the same time.
The courts have made clear that your second alleged offence would count as being on the same occasion as your first and they would only seek to impose a fine and points for the first.
It would be different had you been caught on the same stretch of road at opposite ends of the day, for example travelling to and from work.
However the police are unlikely to remind you of this defence and if it happens to you you need to write to the Chief Constable referring to the law and requesting confirmation that the second alleged offence will be dropped.
In the letter make it clear that you have a deadline to return the NIPs so you should receive a response by return. You will be asked to return both completed NIPs but will only get a caution for the second.
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