Hi need some help
2002 defender 110 excessive black smoke on acceleration
Failed emission test
Confirmed unburnt smoke so over fuelling
Slight loss of power on hills
Would like some advice before I consider injectors to be tested
Maybe air problem just not sure

Any help would be appreciated

Throw some injector cleaner in it and drive it hard

Check the injector harness for oil. Red plug going to the ECU under the off-side seat. It's a cheap fix. Also, have you hooked up a nanocom or similar to read any codes? That would be helpful in pointing you in the right direction.

EGR valve might be clogged/ jammed with oily soot as maybe is the intake manifold, due to faulty vacuum actuator Worth checking the MAP sensor in the manifold and give it a gentle clean with brake cleaner, only held in with a couple of bolts so is easy to remove. Unplug the MAF sensor and see if that makes a difference, easy to check. Clean any dirt off the sensor fitted to the side of the airfilter housing too.
Check intercooler hoses, if they split/ crack/ collapse you can get lots of black smoke and a loss of power.

I'd start with the easy stuff, and then like posted above, check harness plug into ECU for oil and then injectors, copper washers/ O rings etc.

Your airfilter is not wet/ clogged up is it?