Can you spend gift vouchers online?

[popsycal]

HAs anyone done this before?
We have a stack from our wedding and want to spend them in the sales after xmas but I am not sure whether I have the energy to actually venture into the shops!
They are for John Lewis, M and S, House of Fraser and Fenwicks.
Also, do the sales apply to online purchases?
CAn anyone help?

I think it depends on the shop. I had some ELC that I couldn't use on line but had some others (can't remember which ones) that had a code I could put in.