It was Fax’s fifth straight loss in the Qualifiers and leaves them looking at a likely seventh or eighth placed finish.
Richard Marshall’s side arguably lost this contest in eight first-half minutes, with the Broncos scoring three tries via Will Barthau, Alex Walker and Andy Ackers.
With Sammut converting all three, Fax’s dream start, which had seen recalled centre Steve Tyrer score the game’s opening try, rapidly faded to a distant memory at 18-4.
With the wind at their backs, Fax did enjoy enough territory and possession to even things up, with both Brandon Douglas and Ben Kaye going close, but in the end had to settle for a Mitch Cahalane touchdown, the Australian diving on a James Saltonstall kick seven minutes before the break.
Tyrer’s conversion left Fax trailing 18-10 at the break, but - with both teams reduced to 12 men temporarily after Sammut and Rob Worrincy were sin binned following a scuffle early in the second half - it was the Broncos who got the crucial score, Rhys Williams crossing and Keiron Dixon kicking them 24-10 ahead.
Dixon scored himself on 63 minutes, Sammut converting, and when Elliot Kear went over, Sammut again on target to put London 36-10 up, the game was over as a contest.
Fax got some late reward, Worrincy touching down with five minutes to go after good work from Ben Johnston, but it was never enough to influence the result.