35000 miles so far in 15 months

Don't think there's a legal issue as long as tread is within legal limits (unless 1 is a crossply!) but it's not recommended as the grip response could be different from each corner. With a 4x4 it could be worse if they are differing circumferences as it could stress the Diff's more.

Probably best to put the Michelin one on the front so you don't compromise stability or risk causing oversteer and you'll wear it out faster so you can get a matching pair put on, although the Michelin will probably wear slower than the other front continental.

Not against the law as a tyre fitter just offered me a good deal on 3 of one brand and another of another but the tyres must be the same dimensions on each axle.

One thing to check is that the different tread patterns on the different tyres won't cause you problems with the differential/ Viscous Coupling as the system will sense the different frictions of the tyres and try to adjust the diff. This used to be a huge issue with Volvo XC's where if you had worn tyres and then replaced one of them after say a puncture then you had to replace all 4 tyres at the same time. It is similar to transmission wind-up and can do a lot of damage to the transmission

I decided to stick to same brand all round so I expect to be robbed of a few quid

I appreciate that you have failing (failed even) trust in your local LR dealers, but have a check at your local dealership as many are doing 20% discounts at the moment, I don't know if tyres are included in the offer but still worth a try.

Thanks for the tip.