So I've been trouble shooting this and have made progress!

The problem was (and still is) that the score motor runs continuously and lights flash on the playfield.

However, I've discovered that if I trigger the Q relay manually so it latches, the scores reset, the game starts and runs perfectly. However on pressing play to start a new game the same happens again. Kick the Q relay and we're off fine again.

Anyone give me some clues as to some likely causes and where to start checking? Thanks!

So I solved the problem! And it seemed a bit of an odd one.

The Q start relay wasn't triggering. I looked at the schematic and though it might be the switch on the score motor or the reset relay as both feed the Q. However, when I check the voltage on Q it was getting 25V pulses every time the motor went around but still not triggering. I checked the coil as I thought that was faulty - 16 ohms. I then realised I could feel the relay humming each time it was getting a pulse like it was trying to trigger but couldn't. I made sure it could move freely and it was fine. I then tried triggering it with a jump lead direct from the 25v - still no joy. I then removed the spring on the relay and it triggered.
In the end I figured that the spring was too strong for the relay to overcome. The spring looked a little shiny compared to the rest of the stuff so I'm wondering if someone replaced it at some time with one which was too strong. Anyway - I stretched a couple of the coils to make it a little slacker and the machine is now working perfectly! Well - that is perfectly for a machine that has no rubbers in it as they've all rotted! If anyone knows the sizes for these needed for this machine please let me know.

The other work I need to do now is some cabinet repair as parts have been eaten by woodworm.... Does anyone know of a source of wood rail profiles in the UK?