Cark,
Shouldn't be a problem but it obviously depends on the offences. Whilst in most circumstances the rehabilitation of offenders act does a fine job, I'm not sure how it applies to CAA or flying.
Ultimately a PPL is a recreational licence and so I cannot forsee problems for minor thefts/damage or assaults. Repeat drink drive offences or offences relating to a direct breach of a courts wishes eg. driving whilst disqualified are likely to raise an eyebrow or two, but still may not be a bar.
Obviously, anything involving Special Branch or anti terrorist teams is a no-no but last time I dealt with our courts I think even they wouldn't give community service for that kinda stuff!!!
The fact that the offences were some 20 years ago will probably mean they are of little consequence now,
Obs cop