Ok you need to see if its the socket or the plug thats worn, if its the plug you may be able to go to an electrical store and get a replacement for it that you can solder on, something like Tandys should have them or a small independant electronics shop, I doubt pc world or curry/comet or dixons would have them.
Maybe you could just get a new plug and check how secure it feels in the laptop socket, before chopping the old one off and soldering one back on, make sure that you get the polarity right.
Another thing you could try, if it looks like mine and has a central pin on the laptop spcket, is to very very gently try bending it to one side ever so slightly.
Be very careful as you may break it off completely if you try and bend it too far.
This should hopefully make for a firmer contact at no expense or trouble at all