Thanks Guys. I should have given a little more info This is what I did to diagnose the problem.
All four wheels definitely drag, as I had to tow it off the trailer I picked it up with. I suspected the transmission brake so I removed the drum from it. No difference.
I then jacked up the nearside and span the front wheel with a long bar on one of the wheel nuts. The nearside rear wheel began to spin as I was doing this. That suggests to me that its in 4WD. What also happens is that if I jack up one front wheel I can move it above 9 inches in either direction before it hits resistance, it feels the same as a 2WD would if it were left in gear.
The gearstick is in neutral.
I will have a look for the 'protruding bits' you talk about and see what I can do with a can of WD40. The prop shaft idea had occurred to me, I was just after a more permanent fix.
Many thanks again.