Many thanks for all the replies. I've ordered a capacitor off ebay for less than a fiver so worth a chance. If this doesn't work I think I'll go for one of the Wilo ones from Screwfix (I think the Jaguar one is a Wilo). However I can only see this fitting if I remove the four allen bolts and...
I have a jaguar boiler that wouldnt fire up. From reading other threads I suspected the pump. I've taken the pump out and connected it directly to a mains lead. The impeller only starts turning if you give it an initial push and is easily stopped. I think its the capacitor (reading "finger test"...