Content of some sites sometime slow to load-why?

[Murphyv310]

The results vary a lot during the day. They drop a little around four and yesterday it was a bigger drop, the schools were back here yesterday and no doubt due to the sprogs on the net.
This morning I have run another test but with three different "speedtests" Talk Talk tester didn't save the upload speed but came back as 9.8mps.
           

The laptop is connected via Wi-Fi.
I get faster speed in the shed which has a 15 meter Cat5 cable to the router and a Lan switch in the shed!