Only Starts on Second Attempt

My 1.2, 12 valve, petrol never starts on first turn of the key (hot or cold). It cranks over normally but will only start when I return the key and then turn it a second time. Then it starts straight away and idles and drives normally.

I get no codes on my VW code reader and no warning lights. I can hear the in tank fuel pump running for a few seconds on each turn of the key.

I'm wondering if there is a non return valve in the system somewhere that is meant to retain pressure for the next start?

Any ideas on the cause would be very welcome.

TIA.