I have a discovery TD5 (2001). It has started to clunk from below. Car seems ok when travelling in straight line at constant speed but then clunks if wheels turned or car accelerates. is it likely to be a steering fault or universal joint?

OK, you will need to go back to basics here. 'Clunks' could be several things. Issues like a worn suspension bushing, a worn out ball joint, a perished rubber drive shaft joint or a worn driveshaft carrier bearing.
I'll need a bit more information to help. Sound can travel through solid objects which means the sound might not be coming from under the seat. So when EXACTLY does it 'Clunk'? Is it a single clunk or a regular repeating noise? Does it change with road speed? Does it do it when stopped and idling, only when moving or both? Does it happen just as you pull away and as you slow to a stop? Does it happen as you accelerate/brake hard? When you raise the revs to over 2000 is this at idle or as you drive? All these answers will give clues as to where the issue could be.
Use the comment button below with this information and I'll see if I can help you more.

can be anything --exhaust loose ant part in suspension --motor/trans mounts--axles--hubs etc

can of coke in the glove box?

this sounds like a job for a garage mechanic.......

Hi Mitchel

Have your Cv joints checked could be seized and as it drives they gog in and out as you drive over road ways could be very dry of lubricant water got into the boot of one of them you will need to lift on hoist and spin each wheel and see if CV joints and shafts turn true with out the wobble up and down replacing them is best way to go if thats the problem they have recondition cv joints not too expensive way to go
Joe

It's hard to tell, from your description, as to the extent of the clunking.
If it seems to only and constantly occur whenever in forward motion, bumps or not, then I would first check your rear differential, (if 4x4 then your front differential as well).
Check fluid level(s) and if okay, remove cover and check for worn gears and any metal shavings on the magnet on bottom of housing.

Worn gears can toss your vehicle around, any make stomach turning clunks and other awful noises. I've recently replaced a front differential on a 1994 Dakota. It would make same clunks as you describe and a few times would make my back end seem to 'hop' while driving highway speeds. I would check this quickly.

If it only seems to happen over bumps, then your guess on engine mounts or bushings is probably the best guess.

Gear clunking is normal in the Rover's transfer case. It uses straight cut gears - they are stronger, but louder. If not out of the T-Case, check the front driveshaft - another common wear point.

may have a bad transmission mount or engine mount

Could be a wheel bearing or a cv joint

Start by checking the axle half shaft u joints and then the drive line u joints for worn or loose end caps. Also if you have a constant velocity joint on the front drive line make sure the centering ball and socket are not worn. Most people never grease this item and by the time you figure it out it's too late.