Women’s football in England has quietly recorded a series of landmarks this year: the FA Cup final was attended by a record 45,000 people while nearly 2 million people tuned in to watch the game live on the BBC, and Manchester United’s women’s team debuted to record crowds.

This weekend, the English game passes its biggest milestone yet, when its top division becomes fully professional. From the reigning champions, Chelsea, to newcomers Brighton and West Ham, the teams competing in the Women’s Super League will for the first time be facing opponents who are all paid full-time salaries and train as long and hard as they do.

“They’ve got strength and conditioning support and medical support and all those things you want your elite athletes to have,” said Kelly Simmons, the new director of the Women’s Professional Game. “That will help the clubs when they go to play Champions League football; it’ll help England when we go to play in the World Cup.

Beth Mead, 23, a rising star in Arsenal and England’s national team, said: “Anyone can take points off you, that’s the exciting thing about the league. You’ve got to watch it for every team now.”

Quick Guide How the women's game compares with the men's Show Highest salary Women: £35,000 a year (unspecified)

Men: £25.5m a year (Alexis Sanchez) Last year’s top scorer Women: Ellen White (left), 15 goals for Birmingham City

Men: Mohamed Salah, 32 goals for Liverpool Defending champions Women: Chelsea

Men: Manchester City

Highest league attendance Women: 2,570, Chelsea v Man City

Men: 83,222, Tottenham Hotspur v Arsenal

Highest overall attendance (including cups) Women: 45,423, Chelsea v Arsenal

Men: 83,260, Arsenal v Manchester United Photograph: Robin Parker FA/REX/Shutterstock/Rex Features

But despite the optimism about the game’s growing appeal, there are fears the professionalisation of the sport could lead to similar problems to those faced by the men’s game, such as the stark divide between the haves and the have-nots.

More than 150 miles north of where Arsenal’s women train on a fine carpet of grass, one of the FA’s oldest and most celebrated women’s teams is struggling to keep up.

Doncaster Rover Belles (formerly the Doncaster Belles) were one of the first women’s teams to form after the FA lifted its ban on women playing football in the late 1960s. The Belles went on to win the FA Women’s Cup six times since the 1980s and were runners-up a further seven.

The Belles have a fierce rivalry with Arsenal, who in recent years overtook them as the most decorated club in English women’s football. After coming first in the second tier, now known as the Championship, last season, the Belles hoped to once again face theirrivals in the Super League.

But to compete in the top tier, clubs have to field players who are contracted to a minimum of 16 hours – soon rising to 20 hours – of daytime contact a week, plus matches. Teams in the Championship have to guarantee at least eight hours of weekly contact time, plus matches. Also, the clubs have to establish academies to develop young players and coaches.

“We went into the season preparing for a promotion campaign, thinking we can get promoted on merit on the pitch,” said Steven Chicken, a spokesperson for the Belles. But the rules meant the Belles were insteadrelegated to the league’s third tier – they couldn’t afford to pay their players part-time, let alone full-time.

When the players found out the team would be going down a league, they fled. “We’ve lost all of our players,” said Chicken. “Every single member of the playing squad from last year has gone. Our team at the moment is made up almost entirely teenagers who were not expecting to play first team football this year.” And their inexperience is showing – the team recently lost 9-0 to Blackburn Rovers.

The casualty list from the FA’s shake-up of the league includes Watford, Oxford, Sheffield FC, who were forced to withdraw from the second tier for financial reasons, and Sunderland, who are not playing in this season’s Women’s Super League.

“It’s really disappointing to see and really sad,” said Mead, who first made her mark at Sunderland. The club has produced a wealth of England national players: seven of Phil Neville’s Lionesses side, including Mead, began their careers there.

The players are largely focused on this upcoming season, but the buzz of next summer’s Women’s World Cup in France is hard to ignore. England and Scotland have both qualified, the latter for the first time. A cross by Scotland’s Lisa Evans, 26, helped secure the opening goal in their decisive 2-1 win over Albania this week.

Evans, who plays for Arsenal, says the Women’s Super League was crucial in reaching this milestone. “Playing in that professional environment, and training in that professional environment every single day has benefited our national team hugely,” she said.

The changes in the Women’s Super League is generating a buzz abroad too. Julia Simic, 29, left the well-established German league to join West Ham United Women. “I have friends, German players, coming here, playing for different teams,” she said.

The FA wants to increase attendances at senior international matches from 11,000 to 22,000 and double average attendances in the Women’s Super Leage from 1,047 to 2,020. To get there, they need a league that is making money and drawing in fans.

“I call it ‘mainstreaming’ the sport,” Simmons says. “In 10 years, women’s football will be the biggest team sport in this country.” This week, the FA bid to host the 2021 women’s European Championship, which is seen as another key plank in its efforts to grow the game.

But amid the excitement, it’s hard to see where teams like the Belles fit into that future. “Women’s football is changing and we’re not in a position to go along with those changes,” Chicken said. He pauses before adding: “Overall, I feel like the changes are good for the overall profile of the game.”

Simmons remains mindful of clubs struggling to get sponsorship. “We strongly believe what is best for the players – as elite athletes, as England players, as Olympians – is that they are full-time professionals,” she said.

While the women’s game is undoubtedly becoming more like the men’s, Mead is keen to point that some important differences are unlikely to change any time soon. “The girls don’t roll around a lot like the men, they just get on with it. We’re a bit tougher. We’re not drama queens.”

• This article was amended on 10 September 2018 because Sheffield FC, not Sheffield United, had to withdraw from the league for financial reasons.