Joetom LCY-SNN-JFK
The Two Pilot Flight Time Limitations(CAA rules not BA/BALPA) would not allow this 2 sector operation.
A318 T/O weight limitations off short runway at LCY and longer flight times as A318 LRC speed .78 ish as opposed to B777/747 .82/85 mach. Long turnaround SNN due pre-clearing pax for USA Customs/Immigration saving pax time at JFK.
Could put on three F/C but cheaper to slip at SNN and use two.
Bit technical for you perhaps, but you must check your facts before you post on this Forum!