Homeplugs slowing down Internet??

It seems my new homeplugs are playing up. About 4 weeks ago I bought 2 TP-LINK 200mps homeplugs. They're both plugged directly into the wall and all was well with the world.

The last four days the whole internet has slowed down. When I turn off homeplugs - fast Internet again!

I don't understand what's happening. How can the homeplugs slow down the internet? They are supposed to have a low-power after so many minutes of not being used, but they never have switched off - not sure if it's because I run a NAS drive off it?

Any ideas welcome!!

Kit

Okay, have now done speedtests on both - homeplugs turned off and on - the broadband test would not even load with the homplugs on!!

Just a thought (am looking at "noise").....

I have a housephone near the HP - not a mobile charger, just a hands-free phone in it's base - it's the main phone for the house near the phone master socket (which is just the other side of the wall)

Could this affect it?