UK footpaths - is there a map / list?

[LaTristesse]

We'd like to do some walking this summer and have spotted a few intriguing footpath signs round and about. Is there a national (online preferrably!) map of the footpath network, or do you just have to walk them and see where they lead? Ideally I'd like to plan in advance where we're going to start and end!
Thanks in advance

They are shown on ordenance survey maps.

Sorry, pressed send too early. Was going to add that I'm sure you can look at those in libraries, before buying the most relevant to you.

You can use the ordance survery website where you can view other peoples routes. Also countrywalking magazine publishes 24 odd routes per month.
Personally investing in an explorer map for the area at a few pounds is the best thing to do. These have a bigger scale than landranger so you can see more detail.