Actually considering you are in the UK and are probably dealing with low octane and possibly ethanol fuel I would suggest a B6HS or a B7HS at the coldest. A L82C Champion is equivalent to a B6HS.
A B8HS as Muskrat suggested would be fine here in Aus as we get 98 octane fuel with no ethanol in it.
I know we have been over the spark plug thing a hundred times so I can only relate my personal experiences, I have been using NGK plugs for about 40 years and have found them very good. I have had a couple of duds but that would work out to about .005% of the plugs I have bought. The plugs in all my A's are the ones I put in when I put the motors together, some have done 20,000 miles. I clean and gap them whenever I think of it (not very often). So far, fingers crossed, I have never had to change one.