You must use a long reach plug (3/4″). B5ES is correct. Personally I prefer the NGK Iridium IX variety of plugs. It is the first plug which has worked perfectly on my bikes under all conditions. Among other things it gives an extremely hot spark, and needs less voltage. The Iridium IX plugs are more expensive than the normal plugs, but in my view worth it. They have a smaller hexagon (16mm) than usual, and do not take up as much space as the normal series.
The correct Iridium spark plug for the Scott will be BKR5EIX.
It is available from http://www.spark-plugs.co.uk