Car will turn but not start

I have a 1983 opel kadett 1.3s - it has always been reliable until cutting out recently. The engine turns but will not fire, we have replaced the distributor cap, the rotar arm and the electric block [coil?]That leads to the distributor, it still refuses to fire. The wiring on checking seems ok - any ideas? Thanks for replying on problem. The voltage reads 12 volts but general opinion isi it should be higher at positive side of coil. It has an ignition module / block and we have not changed that. Nothing else has been altered or tampered with and car was running until this problem without trouble. It was tested with an electronic tester for spark

Essentially car was in use when trouble developed, I had been on a short drive and was just returning from a shop when it cut out as I turned on to my road, I coasted it to its usual parking space and tried to restart it but it turns but refuses to fire. The engine was changed 3 years ago and the donor car was a Kadett e series [ mine is a d series] circa 1991. Since then the car has shown no trouble, indeed it ran recently from the German border to here in Wigan without the slightest hitch. [ Approx 600 miles]
My initial instinct was that one of the new parts is incorrect [ Opel kadett on ditch plates ] but I am assured that the nova engine is the kadett engine and the new part was matched with the old piece.