There is no starter relay in early Lotus tcs. If it has no relay, then it is probably the ignition switch. You could prove this by running a wire from the battery + terminal to the solenoid where the wire from the ignition switch wire goes Then, just manually energize the solenoid. If the engine cranks, it is probably the ignition switch or a bad connection in that circuit.
If it is a later tcs, then the relay would be a good place to start, and work back through the logic box to all the sensors and ignition switch.
I have an early tcs so I have never seen the later start relay and logic box, so I don’t know the logic.
I have had an intermittent ignition switch. However, it failed by not energizing the ignition while cranking and then energized it when you released the switch from cranking. After many enormous exhaust explosions and countless swear words, I discovered the ignition switch was faulty.
Good luck!