This emphatic Pool One five-point victory means Saints need a win in Limerick that also prevents Munster earning a loser’s bonus-point.

Northampton had to re-adjust their plans hours before the match when England’s new young forward, Courtney Lawes, was forced to drop out with a groin strain.

Rugby director Jim Mallinder shuffled his back row so Phil Dowson moved to blindside and brought in Neil Best at openside.

But Lawes’ injury is not expected to affect his participation in the forthcoming RBS 6 Nations Championship.

French champions Perpignan, whose 9-8 defeat by Treviso in round one remains the upset of the tournament so far, never recovered from the setback and were playing for nothing more than pride at Franklin’s Gardens.

The visitors were awarded a penalty after two minutes for a breakdown infringement, but fly-half Steve Meyer’s kick was off target.

The near-capacity 13,000 crowd quickly made it clear to international referee Alain Rolland that his insistent whistling early in the game was not to their liking.

Nor was the reality that Perpignan had started the sharper and were forcing Northampton to defend inside their 22. It took two tackles to prevent Meyer breaking the line, and a fine clearance kick to touch on halfway from Ben Foden to ease the pressure.

But just when it seemed inevitable that Perpignan would score, Rolland awarded a penalty against them at a ruck, Foden tried to make a sniping break, Meyer tackled him well adrift of the 10-yard gap requirement and was sin-binned in the 18th minute.

Northampton’s first meaningful attack followed, and when the visitors strayed offside, Saints got their first kickable penalty. But Shane Geraghty’s effort flew across the face of the goal.

It took until the 26th minute for Northampton to produce the type of attack which has marked their progress this season, a sweeping move involving Bruce Reihana, Foden and Geraghty. Stopping it illegally cost Perpignan the first points of the afternoon as Geraghty hammered over a 35-yard penalty.

Perpignan should have taken the lead in the 29th when Adrien Plante raced clear onto a ball hacked in behind the home defence and had only to get downward pressure for a try. But Geraghty slid in as the wing hesitated and managed to toe-end the ball away to safety.

That let-off appeared to galvanise Northampton who stepped up the intensity, forcing the French side to defend in numbers, one of whom handed Geraghty a third shot at goal four minutes from half-time, and the England international doubled the score.

Northampton took the initiative from the restart and scored a wonderful try after only three minutes involving England call-ups Foden and Chris Ashton.

Foden made a searing break involving three dummies to pass which bemused the defence before releasing Ashton up the right. The prolific wing scored his 16th try in 17 games, and Geraghty converted.

Saints were now sizzling in the presence of England coaches John Wells, Jon Callard and Mike Ford, and it was the Foden-Ashton axis that shredded Perpignan again in the 55th minute.

Snappy passing between the two saw Ashton hurtling towards the line, but as two defenders lined him up, the former rugby league flyer flipped the ball outside to Dowson to score. Geraghty again converted.

And when scrum-half Lee Dixon burrowed over in the 61st minute, Geraghty converting, the visitors were a spent force.

Northampton captain Dylan Hartley kicked possession away in a failed attempt to cross-kick to his wing, when a pass to his left might have led to a fourth try, but Jon Clarke eased all fears with a dramatic try in the last minute.