Paddy Jackson was still in short trousers and more interested in football than rugby when Ulster defeated Colomiers 21-6 to win the 1999 Heineken Cup.

Tomorrow the 20-year-old will start at fly-half for his province, after having been preferred to Ian Humphreys for Ulster's biggest day in the 13 years since they were crowned European champions. Ulster tackle Edinburgh at the Aviva Stadium for a place in the Heineken Cup final on May 19 at Twickenham, where they would face either defending champions Leinster or Clermont Auvergne.

Ulster coach Brian McLaughlin does not see Jackson's selection ahead of the more experienced Humphreys, who started the quarter-final victory over Munster, as any kind of a gamble. "Nobody wants to miss an occasion like this. It really wasn't easy selecting the squad this week," said McLaughlin.

"Paddy has come in over the last few weeks and done exceptionally well. His performances have warranted selection. It's a very tough call on Ian [Humphreys), who has been exceptional for us over the past couple of seasons, but we felt Paddy deserved a shot.

"Edinburgh are one of the form teams in Europe. They beat Toulouse, one of the kingpins. It will be a big challenge for us."

Ulster, who won both their Rabodirect PRO12 meetings with Edinburgh this season, are without Chris Henry after the loose forward sprained his ankle.

"It's a huge blow for us. He has probably been our most consistent player this season, probably over the past few seasons," McLaughlin said.

As a result, Willie Faloon retains his place on the openside with Stephen Ferris back on the blindside and Pedrie Wannenburg at No.8. Lock Dan Tuohy and hooker Rory Best both return after being rested, while Declan Fitzpatrick continues at tighthead prop after impressing against Leinster last week.

Jackson is the youngest member of the squad and he had just turned seven when Ulster beat Stade Francais in the 1999 semi-final.

"I was living in England at the time, we'd moved over there because of my dad's work, and I was more interested in football," Jackson recalled.

"I'm probably the one person in Ulster that doesn't really remember what they were doing in 1999.

"I may be the youngest player in the squad but I have a job to do at No.10 and I'm very comfortable making the calls. I'm playing alongside Ruan Pienaar, with Paddy Wallace and Darren Cave outside me and Stefan Terblanche behind, so there's lots of experience around me.

"When Brian announced that I was starting, Ian was the first person to congratulate me and told me to ask him anything I wanted. It's great to be able to have that sort of support."

"Edinburgh are a hard team to prepare for. On the one hand their form in the PRO12 has been quite indifferent, but they've been excellent in European competition, where they've not conceded many tries," centre Cave told Ulster's official website.

"We're preparing to meet the Edinburgh team that beat Toulouse – that was mighty impressive."