bob.g: We pay £20 for a (I think) three year subscription to 'Freesat from Sky' for more than 200 channels, including radioYou dont pay a subscription for "Freesat from Sky".
You pay the £20 for a FSFS (Freesat from Sky) card, which gives you access to the FTV(Free to view) channels, i.e Sky 3,Five,Five US,Five US+1,Fiver,Fiver+1 and with an HD box 4HD. So you only need the viewing card should you be interested in receiving those channels.
These channels although free,are hidden behind encryption,hence the need for the viewing card.
Should you still have a viewing card from an ex-subscription(provided it's a current white card) there's actually no need to buy FSFS card as it will continue to give access to the FTV channels even after you cancel.
The card(s) will continue to work until such times as Sky update their encryption,which is why they quote upto 3 years.
The other 200+ channels are FTA(Free To Air) and as the name implies,broadcast un-encrpyted so dont require a veiwing card.Being FTA means they can also be received by any Sky,Freesat or non-platform specific/FTA receiver.