I assume your friend was the registered keeper of the vehicle. A notice of intended prosecution (a NIP) has to be sent to the registered keeper so as to arrive within 14 days of the offence in normal circumstances. However, there are exceptions to this. If the police could not, with due diligence, reasonably trace the identity of the registered keeper so as to be able to send the NIP in time this does not disallow the prosecution to proceed. This might happen, for example, if the DVLA records were not up to date or were inadequate.
With the NIP usually comes the offer of a fixed penalty. If a fixed penalty is not offered (and it will not be if the driver already has 9 or more points or if the speed is so high as to make a fixed penalty inappropriate) a summons will be issued. This must be done within 6 months of the alleged offence.