Centre Jack Power and a close-range forwards effort got Ireland on the scoreboard but England ran out comfortable winners to get their hands on the trophy once more.
England head coach Fletcher said: "We're pleased to get the win, and to be honest I did think that we were the better side, particularly in the second half - but huge credit to Ireland, they're a very good side and made it extremely difficult.
"In terms of our performance, I think that we were much better in the second half, and it's a credit to our lads - they're a tight knit group, and it bodes well for the future.
"We've had a great tour here in Poland, they want the game to grow and this tournament will have helped that. From the hotel to the stadiums, we've enjoyed every minute, which is what it's all about."
Meanwhile, France pipped Wales to third place in an enthralling match, prevailing 31-30 while Scotland finished on a high with a 24-15 victory over Italy.