Hi Duncan,
Are the powerline adapters using the same IP address range - eg 192.168.1.x
Some powerline adapters can be different.
I use a Youview box on a different floor to the router, so did not opt for a powerline solution, but went wireless instead.
I picked up a TP Link WR702N Nano router from amazon for £16 so you may want to look at this option also.
Thanks
Karl.