Despite topping Group C, England came under fire for below-par performances in the group stage after edging past Serbia in the opener before playing out draws with Denmark and Slovenia.

First place in the group means the Three Lions avoided the side of the draw including a lot of the favourites, but even that has not raised morale among the fans.

While Southgate accepted the criticism the team received, he was adamant that the real jeopardy of the tournament starts in the Round of 16.

"[The] reality is that nobody will care about the group stage if you get it right? That is the reality, and of course, we have to deliver it," Southgate said.

"The fact is you go into a different mental state. Everybody knows that knockout football is jeopardy. Everybody knows that, on a given day, an opponent can make it really tough for you. You know the quality of the opposition left is high and so it changes the mindset.

"It is about 'how far can we go?' We are trying to achieve something exceptional. But it is a step at a time and tomorrow is a chance to improve aspects of our game, to show composure in moments.

"The game will take us in different directions at different moments, and you've got to be able to respond and react in the right way in all of those moments."

If England does beat Slovakia, it will set up a quarter-final meeting with Switzerland, which knocked out holder Italy with a 2-0 victory.

Southgate said he was not thinking that far ahead, but that his side do not fear of what awaits it in the knockout rounds.

"It could be another brilliant night to create more memories for our supporters," he added.

"I have played in a semi-final of a major tournament, and managed in a semi-final and a final. Tomorrow, it's about the team progressing.

"We shouldn't have a fear of losing, it's about opportunity. We are trying to reach for something which is a challenge.

"We have lost matches before, life goes on. At that point, when you can handle the worst, you are free to try and go and win the game."