Pre FL S8 cranks but wont start

[Mick]

I have an increasingly annoying problem where my car will crank but not start.

It is intermittent but has been getting steadily worse and is nigh on impossible to replicate except it does it at the worst possible times.

It doesnt matter whether the engine is hot or cold, has been stood 5 minutes or 5 days.

Once it fires it is fine, there are no misfires and runs as it should.

Anyone have any ides on where to start? no pun intended.

Also there are no error codes stored.

Thanks

Mick