Ashton, the joint-leading try-scorer at the World Cup, had drawn a blank in each of his last six Test matches but he roamed menacingly here and touched down twice before the interval and once after.
Although this was not a capped international, a third hat-trick in England colours was a timely confidence boost for Ashton before next month's three-Test series against the Springboks.
The tries were taken soberly too. There was no sign of the elaborate and controversial `Ash Splash' dive he pledged to shelve as "the end of an era".
England hooker Dylan Hartley accepted his own opportunity to make a fresh start with both hands, scoring a try and organising England's forward effort effectively on his return from an eight-week biting ban.
Christian Wade capped a busy afternoon on his senior debut with a try just before the hour and England's win was rounded off by a try from Richard Wigglesworth and two from Jonathan Joseph.
Of those who caught the eye without making the scoresheet, Mouritz Botha produced a barnstorming second row performance and Tom Johnson delivered a strong display on the blindside flank.
England coach Stuart Lancaster still has issues to resolve before the Test series, not least over who should start at fly-half after a rusty performance from Owen Farrell.
England will also be disappointed to have conceded four tries to the Barbarians, one of which was scored by former red rose centre Mike Tindall.
Mils Muliaina scored the Barbarians' first two tries and Biarritz's Pelu Taele added the other late on.
The England touring squad will be boosted by the 18-strong Harlequins and Leicester contingent, who were unavailable after Saturday's sensational Aviva Premiership final.
Phil Dowson captained England in the absence of Chris Robshaw but there will be question marks over his fitness after he left the game on a stretcher.
Farrell, who started at inside centre before switching to fly-half, kicked England into an early lead before scuffing his next penalty shot.
England made a pragmatic start but soon came close to engineering the opening try when Farrell's grubber kick skipped into touch just ahead of Wade.
Lee Dickson then made two sniping runs, perhaps a response to Danny Care's performance on Saturday, before creating the opening try with an inside ball for Ashton to score.
England missed an opportunity when Farrell passed too early to Botha and Brad Barritt then knocked on the offload.
It was a frustrating inaccuracy from England and it cost them as the Barbarians moved up-field and Iain Balshaw's kick fell for Muliaina to touch down.
England responded immediately. Dowson instructed Farrell to kick a penalty for touch so England could exploit their dominant lineout drive, and they executed it to perfection with Hartley touching down.
Farrell scuffed another kick but then supplied the pass for Ashton to score a second try, after a break from Hartley, as England took control.
The complexion of the game changed in the six minutes before half-time and England were back in the try-scoring routine after the interval.
Ashton had already made one break, which was halted expertly by Muliaini, when he hacked on a loose ball to complete his hat-trick.
The Barbarians responded with Muliaina's second try after a moment of attacking quality from Casey Laulala, who drew two defenders and supplied the one-handed scoring pass.
Tom Palmer knocked on with a try at his mercy after good approach play from Botha but England kept the pressure on and worked an overlap for Wade to score.
England began to ring the changes and worked a delightful try for new scrum-half Richard Wigglesworth, who finished off an Ashton break after a delightful pass from Tom Johnston.
Tindall marked his Twickenham return with a try for the Barbarians after taking a quick tap penalty and England will have been disappointed to concede again, to Pelu Taele.
But Jonathan Joseph came off the bench to wrap up the victory with two tries of his own.