Wireless speed issues

Hi, I am after some advice if possible... I have changed provider to sky amd have fibre optic with a max speed of 38Mbps. I have been with them for 1 mth now and ive had an issue from the start. Wired I am getting close to the max of 38Mbps but wireless is very poor - maximum I get it 20Mbps and sometimes it gets as bad as less than 1Mbps.
I have tried every channel and that makes no difference to the speed. I contacted sky and they said its maybe a fault with thw router and sent another out. I still have the same issue.
Does anyone hav any ideas of what I can now try? Unless I am being really unlucky and the 2nd router is also dodgy then its not a problem with sky but something that must be solvable my end... but im out of ideas of what I can try?

Have you ever got faster speeds with the pc that is using wireless?

Also what link speeds are the wireless card reporting?

Hi, thanks for responding.
I should of added... I have been doing the speed tests on 3 different wireless devices - laptop, tablet and phone and get the same result on each. I will get the information you have requested and reply tomorrow.
Also worth noting that im doing all tests in very close range to router with direct sight.
I can only think that its some kind of interference (with it being sometimes 1Mbps and other times 20Mbps but no where close to wired speed)... but cant work out what is interferring.

Do you have any baby monitors, wireless door bell, wireless tv senders in the house or even wireless CCTV?

It does sound like interference. A solution might be to invest in some 5Ghz routers and upgrade your laptops to 5Ghz spec. The range isn't as good though but the speeds are significantly better.