@GavinUK 

HI, if this blackspot requires both wireless and wired connections, I would vote for Deco P9.

While if only a wired connection is required, a pair of TL-PA9020Pkit or TL-PA8033PKIT would be enough.

https://www.tp-link.com/uk/home-networking/powerline/?filterby=5796

You might be also interested in TL-WPA8631PKIT, which is a OneMesh wireless powerline adapter(TP-Link OneMesh™ VS Deco Mesh: What's the Difference?).

It is more suitable if the blackspot is a little far away from the nearest M9 or many walls/barriers in between and when using P9, the wireless backhaul of Deco Mesh from the nearest M9 might not good enough to hold a decent speed.

And with TL-WPA8631Pkit, the signal over electric wires might be transferred a little better.