Category C1 allows drivers to drive vehicles weighing between 3,500 and 7500kg (with a trailer up to 750kg).
Pre 1 January 1997
You should have Category C1 on the back of your driving licence, followed by 107. This is a restriction code that will not allow you to tow more than 750kg. You will need to take the C1+E test to lift the restriction code 107 which will then allow you to tow a combination upto 12000kg.
Post 1 January 1997
You may not have C1 on the back of your licence. To take the C1 test you must have a full Category B licence and be at least 18 years of age.
To find out how to get your C1 licence and more about the test click here