I found this:
The 107 restriction is only found on licences where the C1 category is present by virtue of grandfather rights, ie if you had a full car licence before the new categories came into force (1997 I think) you could drive vehicles up to 7.5 tons gvw and 8.25 tons gtw. This entitlement has no age-related restrictions, so will remain present as long as you have your licence.
The "new" Euro category C1+E allows 12 tonnes GTW but since this is a greater gtw than you would have had with the old car licence, the restriction 107 was invented to reduce the scope of your entitlement. The new Euro C1+E has the same age restrictions as the cat C, ie it needs to be renewed every 5 years from age 45, but this only requires a medical, not a driving test.
So the current situation is that if you have C1+E through grandfather rights you have the code 107 restriction and an enduring licence (ie it doesn't need renewing at 45). To remove the restriction you would need to take a current C1+E test which would give you the full 12 tonnes gtw entitlement (ie remove the 107) but this will need renewing every 5 years from age 45.
If you have the C1+E (107) by grandfather rights and take the C1+E test to get the 107 restriction removed, and then don't renew the licence when the medical falls due, you will revert to entitlement you held through grandfather rights, ie C1+E (107).
If you have taken the C1+E test since the new category was introduced, you will be 12 tonnes rated anyway. This also will of course need renewing every 5 years from 45.
One slightly odd outcome from all this come is you had a full car licence and a full HGV 1 entitlement prior to the introduction of the new licence categories, like I did. Despite having full car and full HGV1 pre-97, my licence now has B+E, C1+E (107), and C+E. It took me a while to work out why the 107 hadn't cleared since the C+E obviously allows me to drive unlimited gross trains weights on the road (subject to Special Types regs etc). The reason is due to the different expiry dates; the C+E now has to be renewed every 5 years (since I am over 45) whilst the B+E and C1+E (107) do not. So if I chose not to renew the C+E entitlement, the 107 restriction would again become effective.
I hope that you can make sense of this, it is actually less complicated than it sounds when you write it down. It does however require a little thought to figure it all out!