Engine locking

Towing digger to work this morning a crunching noise started coming from underneath middle and now its struggling to turn over/wont turn over any ideas ?

Try turning the engine with a socket on the crank pulley. Has the oil pump sprocket bolt been changed to the upgraded one with loctite on it?

Make sure in neutral as well as that sound seems more transmission.

It does sound ike a transmission problem, espescially since you were towing at the time. Hold the clutch in and try it again.
If it starts with the clutch in then releasing the clutch is probably going to make an awful noise and is maybe a broken layshaft in the main box.

Having said that, if it does start with the clutch in, I wouldn't even attempt to lift the clutch. It's sure to be the gearbox which will need to be stripped.
Which gear were you in when it happened? High or low range?