Saratoga:
So, to clarify. If I have restrictions of any form on my licence sub categories I could probably be OK if I have the full ones too?So assuming I had C, D & The E, giving me C, D, CE, DE then restrictions on C1, C1E, D1, D1E shouldn’t cause a problem.
As you rightly say, if you have a full category with no restrictions, you automatically gain unrestricted entitlement to all the subcategories. For example, if you hold full D entitlement, you are allowed to drive a vehicle with 12 passenger seats ‘for hire or reward’, so long as you also hold valid PCV DCPC.
The C1 and restricted C1E, D1 and D1E from a pre-1997 car test are left on your licence, as they are valid until your 70th birthday. If you stopped taking the medicals to keep C, CE, D and DE valid (or ceased to meet the medical standards), you’d still have until 70 entitlement to drive 7.5t or tow with a minibus (not for hire and reward) which cannot be done with just B and BE entitlement.
However, the C1 from a pre-1997 car test may not show separately on your licence if you hold C, because it is not subject to any restriction codes. Think of it as hiding behind your C. It’s the same as B1 often not showing for those that have B.
At 70 you would need to provide an annual D4 medical to keep the C1 and restricted C1E, D1 and D1E valid. Almost every driver that has these categories surrenders them at this point - ‘just in case’ really can’t justify the hassle and expense of an annual medical.
Saratoga:
What about if I had, say, a C1E or D1E but no corresponding C1 or D1? Would that cause any problems?
Theoretically that is impossible - you cannot hold a +E version of a category when you don’t hold the plain category. However, see my earlier comment about categories hiding in some cases and remember this is DVLA we are talking about, so outright errors are possible.
It remains to be seen if there are fewer errors once we move to the new Third Driving Licence Directive compatible photocards in January 2013. The rear of these will have every category set out, with space for start and end dates (or a line of dashes if the category is not held), German style:
However, this is just a layout change. Without changes to procedures and computer software, DVLA may well still make errors they should not. A classic is omitting DE when the licence holder has passed tests for CE and D - the law is clear so the grant of DE should be automatic.
Don’t ask me why B1 is explicitly shown in this case. DVLA seem to explicitly show B1 for B holders who originally acquired B1 along with A (in the days before bike tests stopped giving B1 entitlement) or who took their car test in 1997 or later. B1 never seems to show for those with a pre-1997 car licence who didn’t gain B1 with an A test.
Demonstrating what I said about automatically gaining entitlement to all subcategories, the licence in the picture doesn’t show A1 or A2 entitlement (motorbikes will have two subcategories after 19 January 2013), but does show full A. However, that sample is unusual in that the entitlements have a load of disability-related restriction codes. B appears to have the following codes:* 01 - eyesight correction (i.e. glasses or contact lenses required)
- 15 - modified clutch
- 20 - modified braking systems
- 25 - modified accelerator systems
- 42 - modified rear-view mirrors
That’s quite an unusual set of adaptations - maybe it relates to someone of very short stature driving with pedal extensions and needing a lowered central rear-view mirror, though I wouldn’t be surprised to see a 43 code (modified driving seats) in that case.
A and AM (the new EU moped category) have 01 and 44.6 (motorcycle modified rear-view mirror). The start date of AM is somewhat misleading, in that it’s the first day the category exists (19.01.2013) rather than the day full moped entitlement was gained (05.05.1995; the A test predates the B test)
fklnpq have 118 (organ donor) marked against them, but incorrectly lack 01 - DVLA can’t even get their own example right! 
If you have 01 it should be against every category - DVLA have called in the licence of someone on TruckNet to do this when they realised some categories were not marked 01.
Probably a more common set of disability restriction codes is someone who drives category B using the most common sort of hand controls:* 30 - combined accelerator and brake (or in some cases 20 and 25 for separate modified accelerator and brake)
- possibly 35 - modified control layout (if modified ancillary controls are needed, such as modified indicators, lights, wipers and/or auto transmission controls)
- 40 - modified steering (you have to use a knob if you drive with hand controls)
- 78 - automatic transmission only