You said that you had spent days troubleshooting this problem.
If you had used a meter properly to check for continuity in the first instance, you wouldn't have had to go through the motions of wiring plugs leads etc.
The only mention in your posts of a multi meter was in not feeling the need to use one, but you did show a pic of your totally unsuitable £1 voltage checker, which was the item I was referring to.
You really need to learn to read between the lines, and not
Just accept that you jumped to conclusions based on this being posted to the DIY borad. You assumed that because I hadn't explicitly made reference to various steps or using a multimeter, and I included my voltmeter in shot as I had just checked for voltage - it being easier with the flat-head screwdriver at that moment in time rather than traipse back upstairs to grab my multimeter, you've decided novice.
And, as a week had passed between my starting and cocluding, you have assumed that this was down to DIY incompetence rather than accept my explanation of lack of light and not wanting to work on electrics in the dark.
Through troubleshooting, I've managed to identify the root-cause as a poor terminal design and not, my initial thoughts as a problem with the rose.
Probably the greatest lesson to learn is about buying cheap electrical products from DIY outlets. In this instance it was a simple enough fix, but a lot of light fixtures sold in the UK are of terrible design - mainly a nightmare for compliant installation, but often also stretching the defininitions provided in applicable British Standards.
Two things that amaze me in this life are flimsy insulation provided as protection against electric shock and cheap fibre washers that we depend on to not have flooded homes.
Its actually really frustrating though, this was supposed to have been a quick replacement, as I said earlier, properly jarring when nothing worked.
We've lived in this house for 10 years - as tenants, purchasing from the landlord at the start of November, so we're in the process of making loads of changes which includes building our [long-awaited] extension, moving and fitting new radiators, extending the ring in several rooms, and switching terrible light fittings over.
But its fixed now, lesson-learned - start-off small and work up: so much more easier to adjust terminals
away as well as toward (I only moved toward thinking the terminal wasn't making contact, and then suspected something else).
Its just a shame I placed too much faith in the lampholder. Oh well.
B&Q does make some good quality items, and many of their materials are cheaper but of the same quality as Wickes and TP, so it can be a bit hit and miss in determining between that which is good and that which isn't.