I have a 2003 Polo 1400I

I have a 2003 polo 1400I. Car starts fine and then runs for some time and then cuts out. No spark from the HV Coil. Have also replaced the coil some time ago. Initially thought it was the key transponder so tried the spare key without success. 12Volt input measured on coil but no HV output.
What will a faulty tran sponder in the ignition do? Once it senses the key should it not then carry on running ( Not needed until next start).
Casn it be the pulse transducer in the distributor coil? Have checked he fuel system and that is fine ( Wet plugs no spark?)