Please ignore folks, was me being a biff. My sparkplugs had a smaller hex vs the 20.8mm hex stated on the NGK website, despite having the same BCPR6E code.
Standard ones work fine for me. Sounds like the socket you have is a 'special'.
Access is good so start the plug manually first then tighten with the socket. An off cut of garden hose stuck on the end of the plug can help inserting the plug and twisting it.
