Screwfix call it a "BC Cordgrip Lampholder" BC stands for Bayonet Cap i.e. push up standard is 22mm. Two wires only on most and either way around. Bit of a fiddle getting wires hooked up on plastic lugs to take weight without allowing cores to show once all fitted. Make sure power is off of course. Not allowed to give web page but I'm sure you will find it.
Yes the lampholders are quiet easy to replace, it's just a matter of unscrewing them disconecting the flex and refitting the new one.
You can buy them from all good electrical wholesalers and DIY shops.
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