If the overall journey is WAW to HEL , why not save everyone's expenses and just buy a ticket for a non-stop flight WAW-HEL; 584 miles non stop vs 2067 via London.

Can depart WAW at 16:45 and be arriving in HEL at 19:30 or at 13:05 and arrive at 15:45

Can save the customer the expenses on the WAW-LHR journey by just billing for the alternative flight to HEL and everyone wins and no connection issues and a lot less travel