The Iron had got the better of the Lions in their previous five meetings, including an epic 2009 League One play-off final. But the south Londoners got their own back in style thanks to Henry's first-half cracker and Morison's late double to make it an unhappy 40th birthday for Scunny manager Ian Baraclough.
In the 23rd minute Henry unleashed a low drive from 25 yards which zipped past Joe Murphy and into the corner of the net for the winger's first goal in more than a year.
Scunthorpe could have hit back moments later when Rob Jones met a cross from Eddie Nolan but the defender put his header wide.
But the visitors rarely threatened and with nine minutes remaining Morison charged into the area, jinked past Jones and toe-poked the ball past Murphy from the tightest of angles for number two.
And Morison took his tally for the season to 10 when he lashed a half-clearance back past Murphy from the edge of the box to wrap up the win.
Source: PA
Source: PA