clunking noise only from take-off

There is a sound, clunking/heavier than ticking/ratchet like, happens only when pulling off in 1st gear and more prominent when turning left. Had
a mechanic have a look and he initially thought cv joint but now reckons it could be a chipped tooth in the gearbox! Any ideas?

What year of Jimny is it?

If before 2005 (not VVT/with stick shift 4x4) then is more likley to be the transfer box than the R7me gearbox (T-box chain slipping sounds like you describe), would be under load setting off or if booting it in 1st or second.

after 2005 & VVT/push-button 4x4 would be the R72 gearbox (which seems to be the current fashionable thing to fail).

It's a 2000 Jimny. Will that mean it'll need a new/second hand T-box? If I continue to drive will it eventually seize. Will it be expensive to have fixed. You may notice I have no idea on these things!

Yes (if thats the cause). And yes & no. If the t-box chain fails then it all depends. more likley its slack and gears are worn so would continue to run but get worse and eventually slip all together. If the chain breaks then it could be a brown trouser moment

Take the front and rear props off the t-box, put gearbox in neutral and spin the input prop (intermediate prop) to see what sounds you get from it. drain the oil and see whats stuck on the magnetic plug (but check that the filler plug can be undone before draining it!)

The CV joints are only turning when you're in 4wd, so unless you are using 4wd on the road it won't be that.
I've never heard of a tooth in the gearbox chipping.
When my transfer case chain stretched and started skipping teeth it was quite loud and shook the whole car. It happened when pulling away and on hard acceleration in 1st and 2nd.

not quite into this computer technology stuff, my screen tells me I'm responding to 'Busta' (which I am, but also responding to Riccy....... but hey..........I'm hoping you'll both be able to read if interested). To Riccy, if I was who I dreamed I could be, I would take your advice to the 't' and do the test you advise. I unfortunately don't have much joy when doing things myself mechanically and therefore have learnt to take my vehicle to a 'professional' mechanic anything that only in my imaginary world would be done perfectly by myself! To 'Busta', I also had never heard of a tooth chip in the gearbox making this kind of noise hence me starting this post. Any rough figures on how much this thing will cost me to have fixed? How much time do think I have before I may get this brown trouser moment!!!!!!

Transfer cases are cheap and it only takes a couple of hours to swap. I drove for a few hundred miles before changing mine. If it's slipping out won't fail catastrophically, it will just possibly get worse until you can't move. I took mine apart afterwards and aside from the chain being stretched everything was in good order.