It will be the Saints' first Heineken Cup final for 11 years.

England full-back Ben Foden gave Northampton momentum through a 15th-minute try, and when centre Jon Clarke touched down midway through the second quarter, Perpignan had no way back.

Hooker Guilhem Guirado offered them a glimmer of hope after he touched down just before the break, yet it proved a predictable false dawn as Saints turned the screw up front.

Fly-half Stephen Myler kicked three penalties and two conversions for a 13-point haul, maintaining Northampton’s hopes of a European and domestic double.

They will secure an Aviva Premiership play-off place by beating relegation favourites Leeds Carnegie at Franklin’s Gardens next weekend.

Perpignan offered glimpses of their menacing physical presence and silky running, but at 20-0 behind after 37 minutes the Catalans gave themselves an insurmountable mountain to climb.

And even on the relatively unfamiliar territory of stadium:mk, Northampton were far too good a side to blow such an advantage, leaving France’s wealthy club game without a Heineken final representative for the third time in five seasons.

Northampton’s key players all came to the party – Foden, Myler, mighty prop Soane Tonga’uiha, flanker Phil Dowson and number eight Roger Wilson delivering huge displays amid the rarefied atmosphere of a European semi-final.

Saints smashed Perpignan 34-0 when they visited the east midlands during last season’s Heineken pool stage, and although they avoided a defeat of such magnitude, there was never any serious threat of an away win.

Northampton know they will need to step up a gear against Leinster, whose all-singing, all-dancing approach deposed reigning European champions Toulouse in Dublin yesterday.

Northampton made one enforced change from the side that accounted for quarter-final opponents Ulster three weeks ago, England flanker Tom Wood their absentee.

Wood was sidelined by a leg injury, so Calum Clark replaced him and packed down in Saints’ back row alongside Dowson and Wilson.

Perpignan, whose 11 previous Heineken ties in England had produced a draw and 10 defeats, were captained by France international prop Nicolas Mas, with his front row colleagues including former England Test loosehead Perry Freshwater.

There was little pattern to the initial exchanges, although Foden soon found himself under pressure when he was clattered by his opposite number Jerome Porical.

It served as a statement of intent by Perpignan, underlining that they were not content to sit back and let Northampton dictate the tempo.

Northampton had the first scoring opportunity, but Myler drifted an angled penalty well wide in breezy conditions, yet it proved merely a temporary reprieve for Perpignan.

Dowson blasted through a huge midfield gap barely 60 seconds later, and as Perpignan’s defence attempted to regroup, wing Paul Diggin found Myler, who delivered a scoring pass to Foden.

Myler converted, giving Perpignan plenty to ponder as Saints had started discovering holes in their defence far too easily so early in the contest.

Myler then landed a penalty, leaving Perpignan 10-0 adrift and already playing catch-up on an occasion when their sometimes flaky discipline came under close scrutiny from Irish referee George Clancy.

And matters quickly deteriorated for the visitors as they fell further behind before having a player sin-binned.

Saints centre Clarke made the most of optional Perpignan defending to collect his team’s second try – converted by Myler – before wing Julien Candelon received a yellow card.

And Candelon was fortunate he did not see red after taking out Northampton scrum-half Lee Dickson in mid-air and prompting an anxious moment as Dickson landed awkwardly on his head and neck.

Another Myler penalty took Northampton out to a 20-0 advantage, but Perpignan gave themselves the slimmest of lifelines after Guirado powered over from close range right on half-time, with Porical’s conversion cutting the deficit to 13 points.

Northampton started the second period knowing that one more try would kill Perpignan off, and it almost materialised within five minutes of the restart.

Tonga’uiha almost made it to Perpignan’s line, before Saints skipper Dylan Hartley was denied a try by Guirado’s superb tackle in the corner.

Myler then completed his penalty hat-trick to leave Perpignan 23-7 in arrears, and with Saints having inflicted untold first half damage, they easily closed the game out and ensure all roads lead to Cardiff in three weeks’ time.