Wasting police time (contrary to Section 5(2) of the Criminal Law Act 1967) is a 'summary only' offence. That means that there's a 6 month time limit (from the date that a false report was made to the police) for proceeding to start and the matter can only be dealt with in a Magistrates Court (not a Crown Court). After the 6 month period is up no proceedings can be commenced against an (alleged) offender.
Wasting police time can be dealt with by a £90 fixed penalty or, when dealt with in a Magistrates Court, can lead to a fine of up to £2500 and/or 6 months imprisonment.
However the Crown Prosecution Service might also consider whether a prosecution for perverting the course of justice might be more appropriate. The chances of that happening are increased if
(a) a false accusation was motivated by malice ;
(b) the false complaint was sustained over a period of time, even though the complainant had opportunities to retract his statement ;
(c) a false accusation resulted in someone being charged and remanded in custody ;
(d) a false accusation resulted in someone being convicted before a court ;
(e) the person who made the false report had a history of making such reports ;
(f) a false accusation caused serious damage to someone's reputation ; or
(g) a false accusation was made against a vulnerable person or a person who had been taken advantage of.
Perverting the course of justice is 'indictable only', meaning that it can only be dealt with in a Crown Court and there's no time limit for the start of proceedings. A conviction for perverting the course of justice nearly always leads to a lengthy prison sentence and the maximum penalty is life imprisonment.
If the false reports were simply that a crime had been committed (but without naming a specific person as an offender,or pointing the police towards such a person) the Crown Prosecution Service would probably charge your friend with 'wasting police time'. However if your friend's reports were deliberately 'trying to drop someone in it' then it's likely that he'd be charged with 'perverting the course of justice'. As I've indicated, the choice of charge makes a BIG difference!