The 45-year-old also came in for heavy criticism over selection and tactics during Wales' summer setback in Croatia and Hungary, defeats which left Euro 2020 qualification hopes hanging in the balance.

But Wales took eight points from their final four qualifiers, with Tuesday's 2-0 home win over Hungary sealing their second successive appearance at the Euros, and third in all at major tournaments.

"He'd had stick. But he has delivered, simple as that," Allen said of Giggs.

"He came in off the back of a great manager who had huge success, and it was always going to be tough.

"But he has got us there. I think questions have been asked of everything really – selection, tactics – but nine times out of ten he has got it right.

"That is one of the big reasons we have made it. He has done the job – the ambition and target was to get to the Euros.

"Any way you get there is huge success, and I think a lot of people are going to have to eat their words."

Allen, alongside the likes of Gareth Bale and Aaron Ramsey, is among the survivors of the side who reached the last four in France in 2016.

The 29-year-old, who fell just short with Wales in their 2018 World Cup qualifying bid, has played a crucial role in the current campaign, not only through his own performances but also helping the development of young midfielders Ethan Ampadu, Joe Morrell and Matthew Smith.

"We didn't want to be a flash in the pan, a one-hit wonder if you like," Allen said.

"That World Cup disappointment has spurred on a lot of people. A lot of us are getting older and we realise how precious these chances are.

"The players who have done it before were motivated to get there again and we've banged on to the young lads how good it was.

"I think they were sick of hearing about it and want to see what it's all about!"

Wales will head to Euro 2020 with arguably a more talented squad than they had in France.

Ampadu, Daniel James, Harry Wilson, Joe Rodon and Chris Mepham have all broken into the squad since Euro 2016.

Bournemouth's exciting forward David Brooks, the current Welsh Footballer of the Year, will also be back soon after missing most of the Euro 2020 qualifying campaign following ankle surgery.

"It (qualifying) is different in many ways but just as good," Allen said.

"To do it for the first time was special, but on the back of missing out on the World Cup we're thrilled to go back to the Euros.

"The danger is we did so well last time that the expectation and the bar is going to be raised.

"We've found that in qualifying since France. Teams have made it much more difficult for us and I don't think we'll be so much of a surprise package at this Euros for other teams.

"But we've got players that can hurt any team. We'll go out there and give it all guns blazing."