All the info is here:
http://www.direct.gov.uk/en/Motoring/DriverLicensing/CaravansTrailersCommercialVehicles/DG_4022521
Pretty hard to imagine a car + car transporter with a track car on it that is less this:
If you passed a car test on or after 1 January 1997 you're limited to vehicles up to 3.5 tonnes maximum authorised mass towing a trailer up to 750kgs, or a vehicle and trailer combination up to 3.5 tonnes MAM providing the MAM of the trailer doesn't exceed the unladen mass of the towing vehicle.
@R@tman - you spent >£300 on trailer tests?
As for trafpol - you think they cruise by looking to see if the driver looks younger than 29?
		
 
		
	 
No my employer did 
Test 1     Had to use father inlaws car Shogun Auto and his horse box
             Because Instrutors car was brand new and didnt have the
             bleeping  indicators due to a fault. i failed that test didnt indicate
             to go round a cyclist.
Test 2    Booked this my self using my inlaws shgun automatic and there 
             horse box . I Passed Whoo  however becuase it was in a auto car
             i could only tow with a auto even though i had a manual licence 
             " I DID ASK THE INSTRUCTOR THIS" he said i wont matter as you
              have a manual licence  How wrong he was .
Test 3 Instructor Paid for this one as he was at fault for my restricted  
          licence to towing with automatics . He provided the car and paid for 
          the test i provided the horsebox  . 
          When we got to the test centre the examiner wouldnt take me out 
          as he didn't think the Astra Estate  could pull the horse box so he got 
          vospa to come look and they said it was just legal empty so  the 
          test went ahead and i passed and got my manual licence for towing 
hard work though