Thanks, sorted it. Turns out the nut that holds the blade onto the shaft was on the wrong way around, so the piece that sits snugly in the centre hole in the blade (I guess this is the arbor?!) wasn't doing so, hence it was wobbling. Spinning true now - wouldn't want to have switched it on as it...
I have a second hand Evolution Rage 5S table saw, and there is a problem with the blade catching the riving knife (see video in link below). Something seems to be misaligned but I can't figure out which bit, or whether it can be easily adjusted. Any help would be appreciated...