Basic Disclosures are covered by the Rehab of Offenders act.
Meaning you will pass a Basic Disclosure with flying colours, as long as the rehab act covers it... and that even means serious crimes.
For example, if you comitted a major offence say 10 years ago, and was given a year in prison for it, today, you would pass the basic disclosure (correct me if I'm wrong, I haven't checked in detail as I have no need to!!!)
However, I didn't think the Basic Disclosure was available yet, as they only recently issued the consultation paper.
As for enhanced disclosures, these are only relevent to certain professions involving children as I believe - and as such most employers cannot request them.