Intermittent ceiling light not working - despairing!

[MattB83]

Had a light fitting that flickered - the switch seemed like it didn't click properly so had an electrician change switch and fitting - no problem for a while.

This is a fitting with a switch downstairs and upstairs and occasionally it will not switch on using the upstairs switch, I'll go downstairs and use the downstairs switch and voilà - working again with either switch - it doesn't depend on the position of the downstairs switch. We've recently had an electrician change over both switches (plastic from chrome) but everything has been working for a few weeks until tonight. Also just had an updated distribution board and an electrical safety check done in in case that's of importance.

Is there anything simple to check (or get checked)? Feels like maybe a switch problem - it's working now and it doesn't go off that often (every few weeks) so not sure what too do as fitting and switch have both been changed.

EDIT - first electrician tested all the lights while looking for a fault (ended up replacing a wire) and electricians checked for faults prior to installing new DB - so assuming wiring is OK (reasonable assumption?). Fittings are the fairly cheap MK ones from Wickes.

 

[oldbutnotdead]

There's going to be a loose connection (or more probably a snapped core) behind one of those switchplates.
Power off, switch off the wall, take a photo of the wiring (or otherwise id which core goes where), check terminal screws, make sure the screw is hitting copper not insulation.
Do the same with the other switch. If you find any issues as above then fix them, refix switches, power on, see what happens.
Next stage is as above but disconnect the switch and give each copper core a good tug with a pair of pliers. If one comes out then thats most likely your problem, reterminate (yes terminal block is fine in a backbox to extend the snapped core), refix, power up