Hello and welcome to the mysterious world of Licence entitlements
The Gov't website is far from helpful on these matters. The wording that has been used does not accurately reflect the underlying Act of Parliament which is the definitive document that sets out what you can and can't drive.
Of particular significance to caravanners is the omission of certain key words on the web site, which does give the wrong impression to readers, and in fact in at least one interpretation could lead a driver into committing an offence.
I have made three separate representations to the Web master to point out these errors, for which I have yet to receive a detailed reply concerning the wording, and consistency.
Now to some of the nitty gritty.
When discussing Driving Licence entitlements, you must remember that they apply to the driver and not the car.
The underlying legislation covering licence entitlements always uses a vehicles MAM as one of the key discriminators. Maximum Authorised Mass or MAM refers to the vehicles maximum designed mass or weight. It does not take into account the real weight of a partly loaded vehicle. An analogy would be it's the capacity of a bucket, not what's actually in the bucket.
Over the years the definition of some of the vehicle categories has changed. The B category is a good example and is of course the category that affects caravan users. What your 1988 Cat B licence entitles you to drive is different to what a post 2013 Cat B entitles you to drive. You retain the rights you were awarded, so they don't change even if the category is revised after you achieved your licence. This might be significant for you as I hope you will see.
The Cat B (1997) entitles you to drive a vehicle with a MAM not exceeding 3500kg. You can tow an unbraked trailer of up to 750MAM giving a total outfit combined MAM of 4250kg. Note that is an unbraked trailer and is not particularly relevant to caravanners.
You may tow a braked trailer, provided the combined MAM of tow vehicle and Trailer does not exceed 3500kg. (In safe but simple terms that is the two MAM's added together) BUT the MAM of the trailer must not exceed the tow vehicles unladen weight. (This bit is unique to the Cat B licence issued between 1997 and 2012)
By taking the E extension test, this then entitles you to drive any vehicle with a MAM not exceeding 3500kg, and you can tow a trailer of up to 3500kg MAM giving a maximum combined MAM of 7000kg.
These limits applies to your licence and describes the types of vehicles you can drive. The vehicles you have may have lower mechanical limits which you must obey.