Ford festiva just dies while going down the road

Faulty Fuel pump will do it or breather pipe on fuel tank not breathing.
Coil overheating and braking down when hot ..when cools down away it goes again????
it does sound that its due to overheating BUT a another alternator or distributor wasent needed as nither would give you the problem..So check all above and let me know how you get on Ron

I have seen this problem before. To fix the problem, we have to pinpoint exactly where the problem is (whether it is ignition or fuel related). Do you know how to check for spark or have a spark tester. What I would like to know is whether there is spark from the coil wire (primary) and spark plug wires (secondary) after it dies? If not, then you know its an ignition system problem. Then check the voltage going into the coil at the + and - terminals and let me know what it is. If the ignition is suspect, you should probably have it checked with an oscilloscope so you can see the pattern of the ignition firing. That will dramatically help show what is going on with the ignition firing.
On the other hand, if the ignition spark seems strong after it dies, you need to look to the fuel injectors possibly having intermittent problems. These are tough to diagnose without specialized tools like an injector tester.
Also, have you retrieved your trouble codes from the engine computer? You need to ground the test connector near the drivers side shock tower to get the trouble codes from the flashing check engine light. If there is a stored code, it will tell you where to look for the problem. For example, you could have a bad sensor that is giving the computer (ECA) the wrong information. Once the car warms up, the computer goes into open loop and then problems can begin if its getting wrong information from sensors. There are specialized tools that can test the computer and the car's sensors that I have.