Seti is right that's not going to work you do need to get a switch which is in affect a splitter but it does complicated wizardry which I'm not going to pretend to understand which means you can take 1 Ethernet cable and split it to more than 1 computer.
Basic switches are very cheap and will do the job. . . .. .
HOWEVER I would question what broadband supplier you are with?
Seeing you are from England I know that almost every single broadband provider I can think of will supply you with a router with more than 1 Ethernet port on the back?
It may be worth a call to them to see if there is a free upgrade available!
If you have no luck here is what you will be looking for: ZyXEL ES108A 8 port 10/100 Desktop Switch | Ebuyer.com
I have no experience with that brand or model but the reviews are all very positive and it's the cheapest multi port switch on eBuyer. (Though you may find cheaper on eBay or Amazon).