I can shed a bit of light on the type approval process, but maybe not solve the problem. Any type approval test will involve a "system". The type approval authority (which will be the Vehicle Certification Agency if it was type approved in the UK, and the approval number on the towbar will start "e11" in a rectangle if it was approved to the EU Directive or "E11" in a circle if it was approved to the UN equivalent regulation) will be approached by the towbar manufacturer seeking to get his stuff type approved. He will have a "worst case" meeting with the VCA where he tells them everything he wants the approval to cover and they will tell him the minimum number of tests he needs to do to cover everything. They decide on a "worst case" to test, which will be with a dropper plate if the manufacturer requested it) and the heaviest trailer they specify. The tests themselves are a combination of static pull tests and fatigue tests. It's the fatigue tests that cost the big money because they tie up the machine (and the VCA witness) for a long time while they do their 2 million cycles at some percentage of maximum rated load.
Once he passes all the tests, he and the VCA keep an "information document" detailing exactly what components were tested. If they deviate from that specification, they invalidate their type approval. If your towball breaks, or wears out, you can go to Halfords and buy another one. This too, should have an "e" or "E" mark, so you can fit it without compromising Witter's type approval, because the ball itself will have been put through the same (or worse) tests by its manufacturer. The Freeloader can only tow a couple of tons, whereas the same ball could be bought by someone with a Defender, so chances are, the towball manufacturer will have tested it to 3.5 tonnes (or whatever the maximum is that he wants it to cover). He'd be nuts to test at anything less than the maximum because he'd then limit sales of his product.
The problem comes with the dropper plate, because the dropper plate manufacturer can't afford to get it tested with every towbar at every trailer load. Frankly, I think it's completely nuts that a towbar manufacturer selling towbars for 4x4 vehicles WOULDN'T have included a dropper plate in his tests, but maybe he had reasons for doing so. If that's the case, then yes, you'd invalidate the testing because obviously, you're applying the load to the bolts securing the dropper plate to the towbar via a bigger lever arm which would increase the stress in them.
The thing about type approval, is that it ceases to apply, the moment a vehicle is registered. This is because it is unreasonable to expect the manufacturer to take responsibility for the spec of the vehicle once it is not under his control. A customer could drive it out of the showroom, straight round to his Halfords and fit different wheels, a different radio, different tyres...etc. The same is true of the towbar. So you're not actually breaking any law by invalidating his type approval. You're governed instead, by the Construction & Use Regulations. Regulation 86B in there forbids the use of any "mechanical coupling" (legalspeak for "towbar and associated hardware") that doesn't comply with the EC Directive, so you're no further forward. You've just shifted the onus for compliance from the car / towbar manufacturer to yourself. It doesn't actually say that YOU have to hold an approval (which would be cripplingly expensive) but you ARE responsible for making sure it meets the requirements - and the easiest way of doing that, is by doing what the manufacturer says he's type approved. This applies to any vehicle first used after 1998.
"Use of mechanical coupling devices 86B.
(1) This regulation applies to every light passenger vehicle first used on or after August 1, 1998 in respect of which an EC certificate of conformity has effect.
(2) No person shall use or cause or permit to be used on a road any vehicle to which this regulation applies unless any mechanical coupling device which is attached to it complies with the relevant technical and installation requirements of Annexes I, V, VI and VII of Community Directive 94/20(a) and is marked in accordance with sub-paragraphs 3.3.4 and 3.3.5 of Annex I to that Directive.
(3) For the purposes of this regulation, in a case where a vehicle is drawing a trailer a mechanical coupling device shall not be regarded as being attached to that vehicle if it forms part of the trailer.
(4) In this regulation "mechanical coupling device" shall be construed in accordance with Paragraph 2.1 of Annex I to Community Directive 94/20."
Your Freelander will have been first used after 1998, so you have no getout. (Whereas when I had my 1980 Series III, I just made myself a towbar for it without a care in the world)!
All I can suggest is either:
1. Buy a towbar from another manufacturer who HAS type approved it with a dropper plate or
2. Get a spacer made for your caravan hitch so that you can raise it up above the caravan's A Frame a bit, and fit longer bolts.
Ironically, type approval for trailers is a very recent thing, so you're not breaking any laws or invalidating any approvals by modifying it!
