Try looking to see if the positive connection to the starter motor is loose. Similar thing happened to me, most times it would start fine, then other times nothing but the clicks of the relays, and then try again and it would work. took me till it wouldn't start at all to investigate. Fixed it by the road with a hit to the connection with a big screwdriver from under the car. Got home, tighened it with a spanner, never had trouble again.

Ben Td5 130CC