Hi; do you know whether the Police officer was in a traffic vehicle, or was it a panda car? If it was a traffic officer then they may have used an in car computer such as VASCAR or a hand held laser to measure the vehicles speed. Irrespective of what was used, the officer should have pointed out how they formed the opinion that he was speeding and shown him the evidence (i.e. - the speed read out on the device).
If it was a panda car, then the officer may just have been using the Police cars own speedo; this is often fraught with danger - if he sped up behind him in order to catch up, then he may have incorrectly correlated his speed against your brother's.
If your brother genuinely doesn't know which it was, ring the Police switchboard and tell them your trying to track down P.C. *** (name and no. on the ticket); ask where they work and on which department (uniform/traffic/firearms etc).
This will give you an idea of where you stand; traffic officers tend to be more switched on when it comes to speeding; it's their 'bread and butter'. If it's a panda commander, it may be easier to fight.
Either way, you must produce your documents within 7 days at the station elected on the ticket; if you fail to do so, you commit further offences. Produce them, if you want to fight the ticket, you simply tell the desk clerk that and they will hand them back after checking them and you will receive a summons to go to court later.
There are ways to fight speeding cases, but I suggest you find out more facts and then come back for advice