Worth a go - Robertson himself is a nut job, though his fellow splitter in the 1960s Tim Wohlforth wasn't quite such a case and went a different way.
They're called Spartac
ist btw - the Spartac
us League was a short lived youth group linked to the (British) International Marxist Group 1970-72 (I think) that 'fused' with the IMG - not mentioned on Wikipedia, but documented well enough at the Warwick MRC
http://www.warwick.ac.uk/services/library/mrc/ead/433col.htm.
The history of the SL-Britain on Wiki is quite limited and misses out the small group of nutjobs who joined them in about 1980 from the IMG - somebody called LW was their leader IIRC.
I always used to wind them up on demos when they were selling "Workers Hammer", by asking whether they had a sister paper for those in rural areas - "Peasants Sickle".