Physically disconnect everything from the circuit, IE : Unplug all the appliances. Next find any fused spurs that are running off the circuit and remove the fuses, or switch them off. If you had a recent rewire your distribution board should be marked up, so you can tell which circuit is effected, I am guessing it will be either kitchen, upstairs, or downstairs rings. If you do all of the above and the MCB still won't hold in, you need to call in the electrician who did the rewire, or another competant person.
If you do the above and your ring holds in you have to isolate which item is causing the problem, plug them in one at a time until it trips out, that is the faulty item.
It may be that your recent rewire has replaced your fuseboard with one that includes an RCD, (Residual Current Device) if this is the case the above is still true, but the whole board, or only the none lighting part of the board will trip out.
You need to disconnect / unplug everything as above, see if the RCD will then hold in, and re-connect / plug in everything one at a time until you find the item causing the problem.
CW.