The black plastic fitting just above the white fitting (HepVo trap) where you should see the water dripping down the pipe work is the tun dish, if there is no water staining above this then water is leaking out of the tun dish & running down the outside of the pipes. Dry the area up & give the tun-dish a clean.
As Mike suggests the reason water is dripping in the first place is probably because the air bubble at the top of the cylinder has been lost, turn the water supply off open your hot taps until water stops running from them then follow the instructions (hold the T&P safety valve open until water flow stops & air has been allowed in) then turn back on. Check again for water flow through the tun dish tomorrow, if it is still present call an engineer.
PS. you need to get a cover put back on the lower immersion heater as there are live terminals showing & the wrong type of plastic pipework has been used for the safety valve discharge pipework uPVC solvent weld has been used not the push fit Polybutalene (PB).