Usenet Nutter expressed precisely :
I am going to change that lampholder when I get a new one but is it
possible that has been the cause of the fault...is it possible the
bulb was sitting with only one of the contacts "making contact" .Could
that cause the CB to trip? I was removing some stuff out the cupboard
so may have knocked it on my way out...

The quick easy way to fault find - is to turn everything off, see if it
will then reset, followed by turning things back on again one at a time
until it trips.

The lamp contacts not making contact would not cause the tripping, but
a faulty lamp holder could, a faulty lamp, or a fault (short) on the
flex.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk