http://www.yourrights.org.uk/yourrights ... hotos.html
http://www.homeoffice.gov.uk/police/pow ... gerprints/
I have to say I have NO legal expertise. I just got this from the net.
Currently, according to the above websites the DNA and fingerprints can be kept on file - I think this applies in England and probably Wales too. However, the laws on this are maybe changing.
Scotland has a separate legal system. I believe currently DNA samples / fingerprints are kept indefinitely for those convicted, but only retained from those not found guilty or case dropped, if the person was accused of a serious sexual or violent offence.
Your friend should ask the individual police concerned on their own force's policy with regard to keeping DNA and fingerprints from cases where the charges are dropped or the person was found not guilty.
http://www.direct.gov.uk/en/CrimeJustic ... /DG_196450
This website explains a caution is not a criminal conviction, BUT it does go on your criminal record. This could affect job applications where the person is required to undergo criminal records checks, such as when working with vulnerable groups. Workers such as carers, nurses, teachers and others working with children have to go through this process of background checks.
If your friend is not sure, he should ask for clarification on whether he has been cautioned or whether all charges have indeed been dropped and that nothing went on his record.
I think, from what you say, that it should not affect his application at all. It is convictions for serious offences that the Home Office would be worried about.