Thanks for your advice I put two new tyres on the rear and when I looked more closely at the remaining two decided as they were around 2/3rds worn I bit the bullet. I replaced the front two a couple of days later.
Just not worth the risk of drive train damage and I have a long journey in a couple of weeks time. Plus I have the best of the old ones as a legal spare.
My WJ has just turned 100k miles, I am hoping she does me for another 3 years without too much expense by then she will have racked up 145k and may be looking to change her for the later V6. Diesel 4x4's might be dirt cheap by then with all this anti-diesel talk by the Media.