I'm not sure that the political management of the Lewisham incident by the SWP is the most significant thing about this, but on that point they like everbody else now live in an age in which total control of communications is virtually impossible. I believe it was a solfed member who first mentioned on twitter that the SWP stall had been attacked in Lewisham, presumably as a result of coming across the aftermath in the town centre. Within a few minutes that had been extensively retweeted it and people all over the country knew about it. As a near eye witness (I saw the build up but not the attack) I posted something on my blog the same afternoon etc etc. So keeping the attack quiet would have been impossible, even if they wanted to.
Having heard a bit more about it I now believe this wasn't any kind of disciplined hit. It looks to me like a group of ten or so EDL types went down to Lewisham with the intent to make mischief at the planned UAF event, but probably with no specific plan. They hung around for an hour and then when a soft target presented itself decided to hassle the SWP stall, even then they didn't just steam in but went past shouting abuse, then when they got a bit of lip back a few of them lashed out. I gather that 3 people have now been arrested, as is likely to happen to people who hang around under CCTV cameras in a town centre for an hour and then go home and make crowing noises on facebook about their fun day out.
So while there may be some more sporadic attacks, I wouldn't overinterpret the Lewisham punch-up as heralding the emergence of far-right hit squads of the kind sometimes seen from the 70s to the 90s.