If you go the DIY route and replace the fog-lamp bulbs with LEDs, don’t bother with the eBay cheapies; they’ll progressively fail after a few months. I use (and I think 999to5 does too) these : https://www.autobulbsdirect.co.uk/search.php?mode=search&page=1&keep_https=yes - Cree bulbs from Autobulb Direct.
With the standard mod of adding a relay in the fusebox to activate them when the ignition is on and turn off when headlights come on, the fog-light tell-tale on the dash will come on too. Even though DRLs or front foglights aren’t an MOT requirement for an NC, an examiner spent an age fiddling with the light switches on mine to determine when the DRLs and the tell-tale came on and gave me an advisory on the telltale at the end of it. The moral - Unplug the wire from the relay before the MOT 
What I think is not quite in line with this mod and normal DRL operation is that the DRLs will be on with the side-lights. Which is actually good as you can have front and rear sides on with the DRLs to give extra visibility in gloomy weather when it’s not dim enough to go to headlights.
Going back to the OP’s original question, this may be the thread : Cheap Daytime Running Lights (DRL) fitting on NC