I’ve just having all new tyres fitted to my defender. While it’s on the axle stands I had it in high drive and put it into gear the rear wheels spin ok but the front driver side didn’t spin passages span ok. As though it was binding as with abit of acceleration it span. Turned it off and they all spin freely could it be the front diff at fault or something else. It’s a 1996 300tdi if that makes any difference.

Very unlikely any issues. OS front brake was probably just gripping a bit. Power through the diffs will always take the easy way.
You could check that the brake pistons of that brake all move as they should and there is not a sticky one but as it did spin later likely it is fine.

The 'unwieghted' wheel will always spin first, a slight bit of drag on the brake and the unlocked diff spins the opposite wheel.
I agree with @tottot it's likely that all is fine.

If you haven't changed the oil in the diff's, it's always worth doing.