It's on mileage run forum but maybe interesting for people here, YUL-DME return, with possible stopover in LHR for under $400. And can use those GUV's to DME!
BMI/AC TATL: YUL/YOW-DME $367 (CAD$424) V Booking Code
BD
DAY/TIME FROM/TO CANADA FOR WEEKEND FARES
FROM CANADA -
PERMITTED THU THROUGH SAT ON EACH TRANSATLANTIC SECTOR.
SEASONALITY BETWEEN CANADA AND MOW FOR LOW/OFF-PEAK SEASON FARES
PERMITTED 08JAN THROUGH 28FEB OR 07APR THROUGH 30APR OR
22OCT THROUGH 14DEC OR 25DEC THROUGH 26DEC OR ON 31DEC ON
THE OUTBOUND TRANSATLANTIC SECTOR.