To go back to your original question, you mentioned a spur from the mains.
If you mean an extension cable from the socket it will work.
You need to use a good quality extension cable and preferably not plug anything else in other than the Homeplug, to prevent interference.
(I have in the past used an extension cable with a Homeplug and it does work, even with other things plugged in as well but that was probably luck
)
Be aware that you can get Homeplugs that include WiFi (2.4 & 5Ghz) but it will need to be connected to an ethernet cable as usual.
See example.
http://www.broadbandbuyer.co.uk/products/19721-devolo-9385/Search google for 'homeplug with wifi'
The example is the 1st one I found but there are others.
I know Homeplugs are not liked by some but they do perform a useful function if you cannot route cables. (Or are not allowed
)