First penalty of the afternoon is awarded to Saints from the scrum and that will be a big boost early on.

That ferocious Croke Park atmosphere has just gone down a notch.

Alex Mitchell uncharacteristically takes his eye off the ball and knocks on from a tap back at the line out.

The England nine is usually assured but some early-game nerves perhaps?

Chris Jones
BBC rugby union correspondent on BBC Radio 5 Sports Extra

Listen to the noise around Croke Park!

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Fin Smith gets us up and running...

Here we go then.

Ten minutes behind schedule, the players have made their way out onto the Croke Park turf and we are all set...

Paul Grayson
Former Northampton and England fly-half on BBC Radio 5 Sports Extra

Jamison Gibson-Park has been the accelerant for Leinster and Ireland. He is central to the pace of the game. As soon as there's a breakdown in play he's there.

Alex Mitchell likes to create his own space and run, dart into a gap and make a break as soon as a forward steps out of position.

Both are relentless and superb in support play.

Speaking to TNT Sports, Leinster head coach Leo Cullen said: "The guys have prepared well over the past couple of weeks. It's an amazing location but it’s a semi-final of the Champions Cup so regardless of where it is, it will be very special.

"A lot of kids will grow up dreaming of playing at Croke Park and for our guys to get that opportunity to do it playing rugby is unbelievable."

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Northampton have not been in a Champions Cup semi-final since 2011.

Leinster, on the other hand, are looking to book their place in a third consecutive final.

History favours the Irish side then, but Saints are enjoying a fine season and will pose the 'hosts' questions...

Speaking to TNT Sports, Northampton director of rugby Phil Dowson said: "I think it's right to discuss the historical context of playing at this stadium but now we have to perform. I want to see the lads express themselves as best they can and hopefully we will see that.

"We have shown up until this point we have the game to challenge European sides but we need to be more consistent and more intense in how we do it because we know any errors will be jumped on.

"This is exactly why we play the game."

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Northampton fly-half Fin Smith says his side have had an "eye-opening history lesson" about Croke Park before this afternoon's game.

Saints will be the first English club to play at The Gaelic Athletic Association's (GAA) headquarters.

On Bloody Sunday on 21 November 1920, 14 people were killed when British forces opened fire on a crowd attending a Gaelic football match at the stadium.

The killings took place against the backdrop of the Irish War of Independence.

Read more here.

Just a quick update from the stadium announcer.

Kick off has been delayed by 10 minutes to 17:40 BST...

Chris Jones
BBC rugby union correspondent at Croke Park

Hill 16 is already full with 20 minutes to go until kick-off and the atmosphere is building superbly.

It’s the first time Croke Park has hosted a rugby game in more than 14 years, and what a game it should be. Northampton will come and play - there’s no doubt about that - but can their scrum and breakdown hold up against an Ireland international forward pack? If they do that, and Fin Smith has a good platform, then Saints might be able to pull off the improbable.

But it’s a big if.

As rugby again becomes a temporary tenant at the spiritual home of Gaelic Games in Ireland, both Leinster and Northampton Saints have been studying Croke Park's history in preparation for today's semi-final to be staged at the 82,300-capacity venue.

Leinster have tended to play their Champions Cup knockout games at the Aviva Stadium in Dublin but, with the national stadium already preparing for this month's Uefa Europa League final, an alternative home ground was required.

Croke Park holds the Gaelic Athletic Association's [GAA] biggest games of the season but other sports were historically not allowed to use the stadium.

That changed in 2005 and rugby made use of the relaxation when the Aviva Stadium was redeveloped between 2007 and 2010, though Saturday's contest is the first club game to take place there since Leinster met Munster at this stage of Europe's top competition 15 years ago.

Read more here.

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Plenty of smiles on faces as the Leinster faithful make their way to Croke Park.

Expect a wall of noise from the Dubliners...

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"You have to embrace the right types of mistakes. That is how you get better."

Most coaches urge their players to eradicate unforced errors, but Sam Vesty seems to encourage them.

He is the man responsible for the exciting brand of attacking rugby which has propelled Northampton to the top of the Premiership table and into a first Champions Cup semi-final since 2011.

"I love the fact that there are several ways of playing the game," the Saints attacking coach told BBC Look East.

Read more here.

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Leinster: Frawley; Larmour, Henshaw, Osborne, Lowe; R Byrne, Gibson-Park; Porter, Sheehan, Furlong, Molony, McCarthy, Baird, Van der Flier, Doris (capt).

Replacements: Kelleher, Healy, Ala'alatoa, Jenkins, Conan, McGrath, H Byrne, O'Brien.

Northampton: Furbank; Ramm, Freeman, Dingwall, Hendy; Smith, Mitchell; Waller, Langdon, Davison, Moon, Coles, Lawes (capt), Graham, Augustus.

Replacements: Matavesi, Iyogun, Millar-Mills, Mayanavanua, Scott-Young, James, Litchfield, Seabrook.

Northampton Saints captain Lewis Ludlam will miss his side's today's semi-final because of a shoulder injury.

Flanker Courtney Lawes skippers the Saints in front of an expected crowd of more than 82,000 at Croke Park, with Ollie Sleightholme also missing out after suffering a concussion.

Sam Graham moves to openside flanker, while number eight Juarno Augustus comes into the side that were defeated by Harlequins at Twickenham last weekend.

Irish pedigree...

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English nous...

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It's all to play for in the Investec Champions Cup semi-final as Leinster host Northampton Saints at Croke Park.

Kick off comes at 17:30 BST...

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