Router losing me around 13mb

[#1]

Just done a speed test thinking our fibre was really slow. However, just cabled direct into the router and done a BTwholesale speed test and the results were what I was expecting for our location to cabinet and exchange.
wired i get 36mb download and 15.30mb
wireless I get 20mb download and 10 upload
I noticed this in our old house the wireless was nowhere near cable speeds.
Anyone else experience the same thing with the TG582n

[#2]

Sounds like your computer only has wireless G wifi capabilities, you'd need to upgrade to wireless N kit to get faster speeds over wifi.