The Astronomical New Moon is on Saturday 11 August 2018 at 10.58am. The crescent cannot be seen on this day.
The calculations for London on Sunday 12 August 2018 are as follows:-
Crescent age: 33 hours 33 minutes
Moon lag time: 51 minutes
Crescent altitude: 7.27 degrees
Crescent elongation: 19.49 degrees
The crescent may be visible on this day. Expect 1st Zilhajj 1439AH on Monday 13 August 2018