I asked because the clutch pedal sensor can get out of adjustment which could inhibit the car from starting.
I've only had manual transmission MK3 Foci so I don't know if the DCT has a similar sensor on the brake pedal assuming you have to have your foot on the brake when starting.
We had a similar issue, in reverse, on our brand new Saturn Outlook a decade ago. As soon as we would set cruise control it would drop right back out. Turned out to be a sensitive brake pedal sensor.