Even though England have improved under Gareth Southgate, he wants his team to continue on the upward curve. Photo: Tony O'Brien/Reuters

LONDON England have taken enormous strides since Gareth Southgate took charge but he says his squad still have "everything to prove" as they seek to build on last year's surprise run to the World Cup semi-finals.

Southgate's side began their qualifying campaign for next year's Euro 2020 finals with resounding victories over the Czech Republic and Montenegro to lead Group A ahead of Saturday's clash with Bulgaria at Wembley.

The growing sense of optimism was tempered somewhat in June when England's frailties were exposed as they lost 3-1 to the Netherlands in the Nations League semi-finals.

Victory over Bulgaria, and against Kosovo on Tuesday, will make qualification for next year's finals a near formality but Southgate believes England must not get ahead of themselves.

"We have everything to prove in terms of world rankings. We are competitive against any team but any team is capable of beating us," he told a news conference on Friday.

"We have to strive to improve the mentality of the team, they are hungry to do that. We want to push each other every day in training and take those performances onto the field.

"We have got to take care of qualification. Over the last couple of years we have started to put together an exciting team that hopefully play in a style the supporters warm to."

Under Southgate England, fourth in the FIFA rankings, have turned increasingly to young players with the likes of Manchester United striker Marcus Rashford and Borussia Dortmund's Jadon Sancho expected to face Bulgaria.

"It has been brilliant, they seem to fit right in," Rashford said. "Since Gareth has come in, the younger players have trained the same as the main squad and they fit in seamlessly. The more we get coming in the better."

Southgate said Rashford's United team mate Jesse Lingard is a doubt for the clash with Bulgaria because of illness.

His absence could pave the way for Chelsea youngster Mason Mount to earn his first full cap.