Chris has provided the best link.
It's mainly dishonesty related offences they are reported to take issue with as it tends not to be a good indication of your suitability for the profession.
When I was going through my law degree I remember being told about them having issues with someone who had been caught dodging a bus fare whereas they didn't have the same issue with someone done for assault as it wasn't "dishonest" as such. Not sure how true that was. I believe that Louise Woodward (if you remember the case) went on to qualify as a solicitor.
Heard another story about a group of trainee solicitors doing their pre-qualification course leaving the place they had had lunch without paying - believe they had a close call!
Given the sheer amount of lawyers going to tribunal and firms shut down as reported in the Law Society Gazette each week, seems that many still slip through the net though. Very sad reflection on the profession.