The laws governing what you could drive on a standard driving licence changed on 1 January 1997.
If you want a detailed list of what you can drive on your licence, here is the DSA site for those who passed before 1997.
Here is the DSA site for those who passed in 1997 or after.
The categories which were affected by this change are B+E, C1 and D1 (see below for descriptions). Those who passed their tests before 1997 are referred to as having Grandad rights.
This is the story in brief.
Category A governs motorbikes.
Category B governs cars. This is the category which you automatically have on your licence when you pass the standard driving test at the age of 17 or older and if you passed your test after 1 January 1997 this is the only category you have. This covers any vehicle up to 3.5 tonnes MAM. This is basically up to a small van but it is worth bearing in mind that many standard Transit size vans that you may hire in order to move house, are actually over 3.5 tonnes MAM so you need to be careful. This category also allows you to tow a trailer up to 750kg as long as the total vehicle weight does not exceed 3.5 tonnes. Very few caravans, trailer tents, motorbike or boat trailers come under this weight limit.
Category B+E governs car and trailer. Any category with +E after it denotes a trailer. If you passed your test after January 1997 and want to tow a trailer or a caravan over 750kg you will have to take this extra test. Some normal car driving instructors offer it, but it is generally taught by LGV instructors. The training generally lasts for 20 hours including the time of the test, which follows the format of an LGV test is taken at an LGV test centre, not at a normal car one.
The category C group covers Laden Goods Vehicles - LGV.
Category C1. This covers vehicles up to 7.5 tonnes. If you passed your test before 1997 you automatically have this entitlement on your licence, although you no longer have the entitlement to supervise a novice driver in this category unless you have actually passed a test in this or a subsequent category before April 2010. If you passed your test after 1 January 1997 you have to take a test in this category to be able to drive it. Large vans, ambulances and smaller horse boxes come into this category.
Category C. This used to be called HGV class 2. It covers large rigid vehicles of any size beyond 3.5 tonnes. Some leisure vehicles come within this size category but because they are not laden vehicles, are not covered by the same rules, if you passed your test before 1997. See here for more information.
Category C+E. As I mentioned above +E refers to any trailer so this category covers large vehicles with trailers - basically articulated lorries. To take this test you have to first have passed category C.
The category D group covers Passenger Carrying Vehicles - PCV.
Category D1. This covers minibuses up to 17 seats. Here is the DSA's information site about it. If you passed your test after 1 January 1997 you can only drive a vehicle up to 8 seats including the passenger.
Category D. This covers all rigid buses.
Here are some other useful links:
Licence checking for business
One of many useful motorhome sites