I'm with NathG79 & BigBoy - Definitely gas. The gas meter used to be there. But it was removed/relocated at some point. Do you still have a gas supply? Gas meter in a different location?
There is a way (for a suitably qualified person, i.e. gas safe registered) to determine if the pipe is still live or not, but he/she would not be able to do anything to that supply pipe other than what has already been done to it, i.e. cap at the valve, remove the handle and test for leaks.
However, the pipe doesn't belong to you, it belongs to the gas transporter. Removing the pipe would have to be done by them and considering they didn't remove it when the other pipe was laid (assuming there is another supply), I presume there was a reason they didn't do it in the first place - a reason that would more than likely result in a massive charge to you if you wanted it removed now.
Assume it's live, until told otherwise, and forget about it...
I suppose you could call the transporter (number should be on your gas meter) and report a smell of gas, then they'd come out and check it. Then have a chat with them.
(Sorry I keep editing my post.)