Ireland have beated Georgia (20-10) and France (24-11) to reach the European final, while England accounted for Portugal (62-5) and Wales (11-9) en route to the decider.
Irish teams have been runners-up on four occasions in the FIRA/AER U-18 European Championship (2007, 2008, 2010 and 2012), while the class of 2011, which included current senior internationals Robbie Henshaw and Stuart Olding, won the tournament in France three years ago.
Speaking after Tuesday's semi-final win over France, McNamara said: "We're under no illusions. We'll need to improve.
"Certainly, the pleasing aspect for us as a group, is that we've shown that throughout the last three games against Scotland, Georgia and France and I'm confident we can do that on Saturday as well."
TV3, who have won the televisions rights for the 2015 Rugby World Cup, will air today's Ireland-England clash live from Poland on their sister channel 3e.
Kieran Holden, TV3 Group Head of Sports, said: "It was a very last minute decision but one we couldn't refuse when the pictures were made available to us.
"The Ireland v England Under-18 final is an important game to show so we're delighted to be able to make it available to rugby fans in Ireland.
"It comes in a week where we've enjoyed great success already by securing the rights to next year's Rugby World Cup."
3e's coverage begins at 3.25pm this afternoon with kick-off at 3.30pm in Wronki. A live stream will be available on www.3player.ie/3elive.
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IRELAND UNDER-18 SCHOOLS: Jacob Stockdale (Wallace High School/Ulster); Jordan Larmour (St. Andrew's College/Leinster), Jack Power (Blackrock College/Leinster), Colm Mulcahy (Clongowes Wood College/Leinster), Calvin Nash (Crescent College Comprehensive/Munster); Matthew Gilsenan (St. Michael's College/Leinster), Rowan Osborne (Clongowes Wood College/Leinster); Andrew Porter (St. Andrew's College/Leinster), John Molony (Clongowes Wood College/Leinster), Conan O'Donnell (Summerhill College/Connacht), James Ryan (St. Michael's College/Leinster) (capt), Sean O'Connor (Rockwell College/Munster), Will Connors (Clongowes Wood College/Leinster), Johnny Guy (St. Andrew's College/Leinster), Max Deegan (St. Michael's College/Leinster).
Replacements: Conor McIlmurray (Campbell College/Ulster), Hugo Kean (Blackrock College/Leinster), Conor Kenny (Garbally College/Connacht), Peter Claffey (Garbally College/Connacht), Greg Jones (St. Andrew's College/Leinster), David Duggan (St. Michael's College/Leinster), Jimmy O'Brien (Newbridge College/Leinster), Paul Kiernan (Presentation Brothers Cork/Munster), Oisin O'Meara (St. Michael's College/Leinster), Alan McMahon (Rockwell College/Munster).
ENGLAND UNDER-18: Taylor Prell (Giggleswick School/Leeds Carnegie); George Perkins (Oaklands/Saracens), Lucas Slowik (Filton College/Bristol), Charlie Thacker (Leicester Grammar/Leicester Tigers), Kai Little (Hartpury College/Exeter Chiefs); Harry Mallinder (Rugby School/Northampton Saints), Jack Maunder (Blundells School/Exeter Chiefs); Lewis Boyce (Prince Henry's Grammar/Leeds Carnegie), Ollie Adams (St. Paul's Catholic College/London Irish), Josh Ibuanokpe (Dulwich College/Harlequins), Stanley South (Whitgift School/Harlequins), George Nott (King's School Chester/Sale Sharks), Joe Batley (Hartpury College/Gloucester), Sam Underhill (Sir Thomas Rich's School/Gloucester) (capt), Will Safe (Hartpury College/Gloucester).
Replacements: James Fish (Trent College/Northampton Saints), Owen Hills (Queen Elizabeth Wyggeston College/Leicester Tigers), Jack Stanley (Truro College/Exeter Chiefs), Callum Chick (Gosforth Academy/Newcastle Falcons), Huw Taylor (Old Swinford Hospital/Worcester Warriors), Josh Bainbridge (Prince Henry's Grammar/Leeds Carnegie), Alex Mitchell (Lymm High School/Sale Sharks), Theo Brophy Clews (Abingdon School/London Irish), Joe Marchant (Peter Symonds/Harlequins), Rotimi Segun (Stowe School/Northampton Saints), Cameron Cowell (St. Paul's Catholic College/London Irish).