Accuspark

Never tried them, TBH. As I'm sure you know, the triple electrode doesn't produce a better spark, but it does mean that they last about 3 times as long between servicing, which is why the are quite common on modern cars with long service intervals.

I used to be a fan of NGK, but they don't seem as reliable of late - I've had a new one fail, as have friends - a change in the prodution, perhaps?. I've switched to Nippon Denso from spark-plugs.co.uk/index.php/search/simple/14438.

I'm not sure what grade you need, but the Imp takes NGK BP6ES, and the Denso plugs that I hae in there now are W20EP-U. They cost £1.69/ea inc VAT but plus P+P.

A truly high-performance option might be Denso Iridium plugs (the IW20 is the cross-reference from the W20EP-U). These have a very small tip, which improves flame front propogation. Someone in the Imp club fitted a set to his highly tuned engine and found that the idle was smoother, and the short-term mixture variation recorded by his wide-band lambda sensor was smaller, indicating a more complete, more consistent combustion. I plan to try a set at some stage - but the ~£30 entry price has put me off so far.