@Numpty-AWH1 

Hi,

Provided the Powerline adapter works really well in that location you intend to modify, then a spurred socket should not degrade the connection quality to a point that the Powerline adapters can't establish a connection anymore.
The most likely effect you will see is that the data throughput speed decreases. By what degree is anyone's guess.

However, before you do all the work I suggest you simulate the likely outcome by just plugging an available extension cable of at least same or even somewhat greater length into the socket you were going to spur off from, connect all your equipment to it and then test if it still works to your satisfaction.

  @woozle many thanks will give it a go and post outcome

  @Numpty-AWH1 

Update as promised - Hi so I am running the TP powerline powered via a 4 way extension cable and it's working fine so have not bothered with a spur.