England manager Gareth Southgate knows his young squad have come a long way since paper aeroplanes were thrown onto the Wembley pitch - but warned the World Cup semi-finalists must continue to improve.

Southgate's side face Spain in their opening UEFA Nations League clash on Saturday night before taking on Switzerland at Leicester's King Power Stadium in a friendly next week.

The Three Lions' run to the semi-finals of the World Cup in Russia united the nation earlier this summer, restoring public affection after several tournaments of disappointment.

Southgate, though, believes it is the time to look forward and move on from the defeat to Croatia in Moscow.

Southgate says it's time to move on from Russia (AFP/Getty)

"Over the summer (at the World Cup) you are looking for results, now it is about developing the team and improvement, looking at how we play, the tactical detail and testing ourselves against some really top teams," the England manager said.

"It is great we have got a full house (at Wembley) and we can step out in front of our own fans, and everyone will feel the appreciation - but now it is about the next challenge.

"The summer is finished, we've got to move forward, continually evolve. Sport doesn't stand still and you have to improve. What comes next is the most important thing."

Southgate continued: "It is brilliant that there is this excitement around international football because one of our ambitions is to improve that connection with the supporters, so the impact of the team over the summer was really pleasing.

"A year ago we had paper aeroplanes landing in the pitch when we qualified, so that is great credit to the players."

Spain failed to make it past the last-16 stage at the World Cup after being beaten on penalties by hosts Russia.

But Southgate is not expecting an easy ride as the former world and European champions look to begin a new era.

"There will definitely be some differences that (new head coach) Luis Enrique wants to impose. They have some wonderful footballers and it will be a tough game," he said.

Southgate is wary of the threat Spain pose (Getty)

England captain Harry Kane secured the Golden Boot as leading scorer at the World Cup with six goals.

The Tottenham forward is set to wear a special pair of boots at Wembley to mark the achievement as he receives the personal trophy before kick-off.

Despite the plaudits coming his way, the 25-year-old Englishman believes he still has work to do before being compared to the likes of Lionel Messi and Cristiano Ronaldo.

"They have set an unbelievable standard over the last few years but they are the heights we all want to reach," Kane said.

"To finish a World Cup as top goalscorer was something I was extremely proud of, but now it's on to more things."