Having knocked on the door of the knockout stages only to invariably be denied entry at the final stage, so it comes to pass that Leinster are the only team mathematically assured of a quarter-final place in the Heineken European Cup after the first four rounds of the pool stages. They've merely emulated their achievement of eight points two seasons ago, which proved insufficient. But such is the way of things.

To have accumulated four back-to-back wins in a group containing one of Wales' top two sides on current form and by common consent one of the leading pair in France (Toulouse are the reigning French champions) is a hell of an achievement. So what that other results in the pool panned out in Leinster's favour? Good luck to them.

At the risk of being repetitive, Leinster are assured of a quarter-final place because in the event of two sides finishing level then firstly the match results and then the try tallies in the matches between those sides are taken into account. Only Newport can equal Leinster's tally of eight points in Pool Six and as Matt Williams' team have beaten the Welshmen back-to-back over the last two weekends, that means they cannot be overtaken.

"That's great news for Irish rugby," said Declan Kidney with genuine satisfaction for Leinster's achievement, while another in the Munster camp said: "Great. Now they've got to go and get a home quarter-final." This also was genuinely hoped for.

In three weekends' time the Munster-Leinster rivalry will be renewed in the Guinness Interprovincial championship and while Leinster's improving stock this season has probably intensified the rivalry even further, by and large it's a healthy one. Who knows, in addition to the two scheduled interpro meetings they could meet a third time (in the Celtic League) and perhaps even a fourth.

Indeed, I can't imagine the support and goodwill that exists between the provinces can be matched by club sides in, say, England, France and Wales.

The four provinces have tended to feed off each other's successes right back to the darker campaigns of about five years ago. It's worth recalling that Connacht's success in what is now the Parker Pen Shield four seasons ago with their stunning wins over Northampton especially was the catalyst for the ripple effect which has continued to this day.

Williams deserves immense credit for adding the missing pieces to a complex Leinster jigsaw and enabling them to fulfil their undoubted talent more than ever before. First and foremost he has shown a willingness to delegate and share responsibility, and the work which Alan Gaffney has done with the backs, along with Willie Anderson's and Roly Meates' work with the forwards, have all been part of the mix.

For years and years, seemingly dating back to Paul Dean and Fergus Slattery, outhalf and openside flanker were Leinster's problem positions. Unlucky to lose Emmet Farrell last season and mindful that Liam Toland's army commitment would be more time consuming this season, Williams handsomely solved both problem positions by bringing in Nathan Spooner and Keith Gleeson.

Australia's and New South Wales' loss is Leinster's gain, for the province has been blessed to acquire a top quality and true openside flanker with Irish ancestry in the shape of Gleeson, particularly bearing in mind they probably wouldn't be able to compete with some of the French, English and Welsh clubs who are backed by sugar daddies.

It's funny how certain outhalves suit certain teams. Spooner wouldn't be the quickest outhalf in the world game but Leinster's need was not a game-breaking, sniping number 10, more a controlling, calming presence who takes the right options, takes his backs up to the gain-line, makes his tackles, and knows how to close games out.

Williams lauds the fact that both players are still young and hungry, rather than over here for an end-of-career pay-off cheque.

In a squad long on talent but previously short on leadership, it's quite conceivable that, without these two, Leinster might have buckled in either or both of the games against Newport when the going got tough. Admittedly a slight concern is Spooner's place-kicking ratio. That said, Spooner underlined his match-winning temperament with those long-range penalties last Friday.

He's the link between a dynamic back row and pacey outside backs and, more than most sides in Europe, Leinster have the capacity to strike stealthily any time, anywhere and from any place on the pitch. In setting a provincial record of 11 straight wins they have scored a phenomenal 47 tries, of which a freaky 28 have been scored by Brian O'Driscoll and the backs outside of him.

We always knew they could score tries of course. As significant though has been Leinster's much improved defence, which Williams has made the bedrock of their performances. Caught up in a game of pyjama rugby in a rare 40-minute blemish away to Bridgend in the Celtic League, at which point they had conceded four tries, a furious Williams kept the players on the pitch doing drills and demanded a more structured, tighter second-half display.

In the four and a half games which followed, prior to last Friday's match in Rodney Parade, Leinster conceded just one try, which was pretty much an unstoppable French effort by Toulouse winger Michel Marfaing - the leading try scorer in the competition's history. The concession of two tries last Friday constitutes only the second time in 11 games this season that Leinster have conceded more than one try.

Furthermore, there is an underlining belief running through the entire Leinster set-up that they have the strength in depth to cope with a campaign which could conceivably stretch to 22 matches. That is why the importance of those apparent footnote Celtic League wins in Llanelli and Swansea were so important to the group's feel-good factor.

It is, as the Munster man stated, imperative that Leinster go on and earn a home quarter-final. None of the ultimate Heineken Cup champions have ever taken an away route in the quarter-finals. Indeed in the last three years all 12 quarter-finals have ended in home wins.

For that to happen then most probably Leinster will need to win at least one, and possibly even both, of their remaining away games to Newcastle and Toulouse in January. Both are renowned home sides and anyone who saw the highlights of Newcastle's Tongan-tornado Epeli Taione, a remarkable mix of 18 stone, 6 feet 4 inches and centre three-quarter pace nominally employed in the back row, cut a swathe through Toulouse in Kingston Park at the weekend, will appreciate how difficult that is liable to be.

gthornley@irish-times.ie