Do the police have time limits

[Silverninja]

A friend of mine got into a fight with his girlfriends ex-boyfriend who had been threatening to kill her.
this happened in december 07 & my friend did his best to avoid the situation & say's he never threw the first punch! but the ex-boyfriend ended up with a cut above his eye! my friend has recently received a letter from the police stating that they are investigating an allegation of assault, my question is do the police have time limits on how long they have to investigate or press charges? considering that this all happened about 6 months ago!

[New Judge]

Common Assault is a "summary" offence and there is a time limit of six months to begin a prosecution. More serious ("indictable") offences have no time limit.

[ELVIS68]

Time limits for police...

If you ring them for a burglary... about 24hours

If you ring them to say you`ve just shot a burglar...5 minutes

[Silverninja]

So what would classify as a more serious indictable offence? Just so he knows where he stands, Does his fight come under common assault! Or could it come under an indictable offence seeing as the ex-boyfriend suffered an injury?

[Silverninja]

Also as the incident took place 6 months ago could he just ignore the letter as the time limit to prosecute has just about run out?