So recently bought a 2003 LX Fiesta but it only come with the spare key. Purchased one online off ebay with the fob on etc for cental locking & got it cut. Now I've done the key in ignition and turned it 4 times till it beeps. The central locking now works brilliantly with the new fob but the new key won't start the ignition. What am I doing wrong? Does the key itself need to be programmed into the car? Its odd how the fob on the new key will work but not the key itself 

Please help if possible. Thanks in advance 

Yes the immobiliser needs programming. Make sure your new key came with the chip inside, more often than not the eBay ones don't come with an immobiliser chip. You'd probably find that inserting the new key into the ignition and holding your current key very close to the barrel will start the car.

It does. It's got the little black chip inside. Like I say it's weird the central locking on the new fob works but not the key on it haha 

Yes in that case you just need the immobiliser chip programmed into the car. Programming the fob to unlock the doors is not the same as the immobiliser. A local auto-locksmiths can do this for you.

You can only use the method you described if you already have 2 working keys and are adding a third.