Thanks. Interestingly, it doesnt slip without the e-assist motor powering up. I rode it gently on the flat and the gears engage. On a hill, it slows to a stop, your legs are just not strong enough to keep it moving, but despite strong pressure on the pedals still no slipping.
So I'm hoping the hub is ok, but something about the motor engaging causes slippage. As @MCamb hopefully just the freewheel pawls.
I'm a bit stranded as I have a new job on site tomorrow and will have to take my tools on the train, all my bike stuff is at my lock-up 10 miles away, don't really want to disassemble it in my front garden.