Its not just the cost of getting CI+E, I hear the failure rate is very high! So I can understand why you got **** on.
I've lifted this off the DVLA web site...
'Subcategory C1: Medium sized goods vehicles 3.5 - 7.5 tonnes MAM
Subcategory C1 vehicles may be coupled with a trailer up to 750kgs MAM allowing a combination of up to 8.25 tonnes MAM. But unlike category B, the 750kgs MAM trailer weight limit is an absolute limit.
In order to gain this entitlement category B licence holders have to meet higher medical standards and pass both theory and practical tests for subcategory C1.
Subcategory C1+E: Medium sized goods vehicles 3.5 - 7.5 tonnes MAM plus trailer over 750kgs MAM
Subcategory C1+E allows vehicles to be combined with a trailer over 750kgs MAM provided the combination does not exceed 12 tonnes MAM and the laden weight of the trailer does not exceed the unladen weight of the towing vehicle.
In order to gain this entitlement category B licence holders have to pass further tests - subcategory C1 (theory and practical) followed by C1+E practical. There is no subcategory C1+E theory test. It will not be possible to go directly from category B to subcategory C1+E.
Because EC regulations limit drivers aged under 21 years to driving vehicles or combinations which weigh no more than 7.5 tonnes MAM, drivers under the age of 21 are not allowed to drive subcategory C1+E vehicles up to 12 tonnes MAM. But 18 year old drivers are allowed to take a test for subcategory C1+E which will allow trailers in excess of 750kgs MAM to be towed. Entitlement is limited to a combination weight of 7.5 tonnes MAM until the driver reaches 21 years, at which time the balance of 12 tonnes MAM entitlement automatically becomes effective'.
Just so we know.