@aklondonuk Hello, 

Please make sure  powerline units are plugged into the Wall socket directly, not via  power strip, and you could try a different wall socket for the powerline unit and see if the powerline rate could be higher. Speed will get reduced while signal being transmitted through powerline . The real speed is closely related to the powerline rate and also the speed coming from router.  In the actual household environment, real speed test could be 20% to 30% of the Powerline rate and also capped by ISP bandwidth or router speed. Here is a related FAQ explaining the Powerline Rate and Actual speed of the Powerline Adapters: 
https://www.tp-link.com/support/faq/2928/

Powerline rate is an indicator of the powerline environment, from your photo the powerline rate is 105Mps, which means powerline environment is not so good and  powerline devices may get unstable/ slow speed. You could follow this instruction and remove the things that may affect the power environment:
https://www.tp-link.com/support/faq/409/