I'm looking at this blade by Dakin Flathers, mainly because it's a few quid cheaper and I can get next day delivery with prime. It's M42 so should be the same, right?
Fitted the new blade and all is good.
There were a number of teeth missing on the original blade which is probably why it kept jamming. I also adjusted pulley alignment and it's stopped jumping off.
Thank you to everyone for the help.