Disclaimer: I think the information below is correct at the time of writing (November 2000) but I don't guarantee it.
The process of getting a Unimog (U1300L) campervan correctly registered, licenced, and tested in the UK is relatively straightforward when you recognize that the rules governing registration are quite independent of those governing testing.
When I purchased my Unimog it was already registered as a "2 Axle-Rigid-Body Agric. Tractor". From the suppliers point of view this registration has lots of advantages. Its cheap (only £40 Vehicle Excise Duty/Tax Disk per year), you can sell it without an MOT Test Certificate and off-road you can (under some circumstances) use duty free diesel. However to use a Unimog as a campervan on the road in the UK you must (in this order) get it MOT tested, register it and pay the Vehicle Excise Duty.
Before you can register a Unimog campervan in the appropriate taxation class you need a valid MOT test certificate. When you try to get a Unimog MOT tested you may have a problem. What you want is a Class IV test (this the same type of test that is applied to Private/Light Goods vehicles) but very few ordinary test centers are equipped to test something as big and heavy as a Unimog. Those test centres that can handle a Unimog may want to test it as a goods vehicle. However if your Unimog is adapted for use as a motorhome then for the purposes of MOT testing it is Class IV. An ex-German army Unimog U1300L should pass an MOT test in this class without major problems. The definition of a motorhome is reasonable and relates to having a bed, table, seats, storage etc. Getting your Unimog campervan "shell" MOT tested as Class IV may be a more difficult than getting a fully finished vehicle tested.
Warning: This section is awaiting written clarification from the DVLA. The decision about which taxation class a Unimog campervan fits is formally made by your local Vehicle Registration Office (VRO). Following conflicting advice from my local VRO I asked for a definitive ruling from the DVLA at Swansea and was told (on the 2nd November 2000) that my Unimog U1300L (as converted) should be taxation class TC10 Private HGV (not TC11 Private/Light Goods). I was also told the body type should be Motor Caravan (not motor home or campervan). The only consequence of this classification is that I must pay £165 PA rather than £155 PA.
The total weight of your conversion should, of course, be less than 7,500 kgs both because this is the maximum permitted weight of the vehicle (Unimog U1300L) and the maximum weight of vehicle you can drive with an "ordinary" UK C1 category driving licence (this assumes you passed your test before 1997(?). If you passed your test after 1997 you may not be allowed to drive a 7.5 tonne Unimog on the road in the UK.
Last updated 2nd December 2000.