A caution is a conviction. never except them, they are only given when the CPS wouldn't bother to prosecute. Also they help boost the polices percentages of convictions
Sorry but that is utter rubbish.
To be given a caution there must be evidence the person is guilty, and they must have admitted to the offence. The purpose is to divert lesser offences from the court.
A caution is NOT a conviction, and is not recorded as such.
A full explanation is on the home office website which is probably worth a read rather than following some of the advice on here...
Cautions, penalty notices and other alternatives | Home Office