I actually know someone in this position who asked my advice on this very problem - regretting fully stuff they'd done when young and stupid. Basicaly, the paln now is that he or she is going to get a low paid, low skill job first - one where they don't care about a reference - (theres lots of those about). They are going to do that for a few months then go to another one - then after a few months of that look for a decent job, but now they will have references available from 2 previous employers. Certain jobs are exempt from the Rehabilitation of Offenders Act 1974- such as working for the police or nursing etc - for those positions you MUST declare previous convictions and they check anyway of course. But for 99.9% of jobs, the law quite clearly says that after a certain time convictions are "spent" and thus need not be declared (unless for certain posts like mentioned above - which is fair enough of course for the protection of the public). This is because of course that real aim of the criminal justice system is to get people back into normal working life afterwards so they can be productive members of the community. Obviously, an individual makes thier own decisions, so if some offences bar them for life from certain posts, then they really have to consider that *before* committing crime (I know, personal responsibility is an unfashionable idea in our PC age!). Anyway, there *are* ways back into work - Ive seen it done many times in the field I work in - for full details of the timescales and a good explanation see:
http://www.lawontheweb.co.uk/rehabact.htm