Veteran Gallen has now hit 17 goals for the Hatters this season
Kevin Gallen's hat-trick helped Luton to keep up the pressure on Blue Square Premier title rivals Stevenage as they hammered already relegated Grays.
Tom Craddock opened the scoring with a header before Gallen hit a quick-fire double with two good finishes.
Craddock then fired home from close range as Luton led 4-0 at the break.
Gallen completed his treble soon after half-time, heading past the helpless Glyn Garner before Liam Hatch completed the scoring with another header.
Veteran striker Gallen's opening goal was his best of the afternoon as he latched onto Keith Keane's free-kick to smash his shot past Garner from 25 yards.
The Hatters could have already been 6-0 up by the time Hatch completed the rout, but substitute Craig Nelthorpe's shot hit the post.
Luton have now won nine consecutive games in the Blue Square Premier and have closed the gap on leaders Stevenage to two points.
Richard Money's side have been in ruthless form in recent weeks, hitting 28 goals in their last six games.
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