got 53 diesel auto disco when cruising along at 50 mph and putting my foot down to overtake it hesitates 3 or 4 times before picking up and accelerating normally it runs smooth at all other times and drives fine any ideas ?

Check the wastegate arm on the turbo is free,they sieze up and cause an overboost situation which the engine ecu doesnt like so it cuts output - the boost dies,the ecu gives the fuel back,boost goes back up to overboost and it cuts again.
Most TD5's can be made to do this if you drive them hard enough.
Disconnect the arm on the turbo to check it,free it off with WD40.If it still sticks the arm needs to be partially removed and the core plug in the back of the turbo needs removing to allow removal of the rust and carbon that cause the problem.Its not an easy task,it requires cutting,welding,slidehammering etc.But it works and is cheaper than the LR way which is to bolt on a new one !