Sir Philip Green is battling to rescue his Topshop empire from collapse and time is running out.

The billionaire’s Arcadia group, which employs about 19,000 people, is desperate to secure a rescue restructure that will involve the closure of about 50 of the group’s 570 British stores.

If a deal cannot be agreed well before the group’s next rental payment in late June, Arcadia – which includes Topshop, Dorothy Perkins, Miss Selfridge, Wallis, Evans and Burton – could face administration.

Green, who has not been in the UK since October, is said to be keen to wrap up an exit from the group he bought for £850m 17 years ago. With his reputation in tatters after the collapse of BHS and accusations of inappropriate behaviour, the entrepreneur has lost his appetite for the British high street.

One alternative to administration for Arcadia could be an immediate sale, but industry experts say a deal is highly unlikely without a process to cut costs and reduce the burden of the group’s pension black hole – which comes to £537m. Even then, only Topshop is likely to attract serious interest, although the likes of the Edinburgh Woollen Mill owner Philip Day and Sports Direct boss Mike Ashley might be tempted to pick up the smaller brands if they went bust.

Arcadia had hoped last week to announce plans for a restructuring known as a company voluntary arrangement (CVA), which would enable it to close stores and cut rents. But the board is struggling to secure enough backing from landlords, 75% of whom must approve the changes.

The process is particularly complex for Arcadia as it involves up to eight corporate entities, each of which would be subject to a vote by landlords and other creditors.

In order to back the deal, landlords are demanding Green put up significantly more than the £100m in loans that he has so far promised to invest in improving Arcadia’s stores. It is understood they also want the investment in cash rather than loans. The landlords are pressuring Green to revamp stores and upgrade the entire business for modern digital and delivery services so that Topshop – and sister chains including Outfit, Wallis and Miss Selfridge – can compete with H&M, Zara, Asos and Boohoo.

A branch of Topshop in a London shopping mall. Photograph: Alamy

Green has offered landlords a 10% share in the proceeds from any future sale of the business – but they are holding out for more.

As part of the rescue deal, Arcadia also wants to halve payments to its pension fund to £25m a year, only two years after agreeing to up them to £50m.

The scheme has a deficit of more than £537m based on the company continuing to operate. But that would rise to as much as £750m if Arcadia were to go bust, and pension regulators and the fund’s trustees are likely to focus on that figure. The success of the CVA is dependent on their backing, as the fund is a major creditor.

Arcadia has offered to hand over to the fund the freehold of Topshop’s flagship Oxford Street store in central London, but that property, which is worth about £400m, is heavily mortgaged with only about £100m of equity on the table. Currently trustees and regulators are holding out for a better deal. Arcadia declined to comment on its restructuring plans.

After years of underinvestment, Arcadia’s sales slid by 5% in the 12 weeks to 10 March, according to market analysts Kantar. The overall clothing market increased sales by 1.4% over that period.

Analysts say the group’s sales started falling in the summer of 2015, since when its market share has slid by 1 percentage point to 3.2%. This may not seem a big change, but it reflects millions of pounds in lost turnover. One analyst who declined to be named said: “[Arcadia] is still miles behind the curve. It’s a pretty ugly picture.” Retail and property insiders describe many Arcadia stores as unexciting or shabby.

Patrick O’Brien, a retail analyst at GlobalData, said: “The brands have been underinvested over many, many years and have lapsed into irrelevancy to their target market. If you look at Miss Selfridge or Dorothy Perkins, these are very outdated brands that really don’t resonate with the sort of shoppers going online to Asos or Boohoo.”

BHS, Oxford Street, London, shortly before it closed in 2016. Photograph: Andy Rain/EPA

In relation to the group’s online business he said: “Nothing has been invested to the degree that they can compete with the likes of Asos or Boohoo. It’s just another website rather than showing innovation.”

Over the years, Green has taken millions of pounds out of the business in dividends, loan payments and property profits. The Green family famously took a £1.2bn dividend from Arcadia in 2005, just three years after buying the company.

According to accounts for Arcadia’s parent company, Taveta Investments, Tina Green, Sir Philip’s Monaco-based wife, was paid nearly £220m in interest and loan repayments relating to the now collapsed BHS chain between 2009 and August 2017. The Greens, who bought BHS in 2002 for £200m, sold it to their Arcadia group in 2009. The chain was then sold to a group led by a former bankrupt, Dominic Chappell, for £1 in 2015 and collapsed about a year later. Green has defended his stewardship of BHS, saying he invested “substantially” in the business.

Including the BHS payments, the Greens have collected at least £356m from Taveta since 2009, including £53m for the purchase of BHS’s Marylebone House head office, and nearly £72m in rental payments largely relating to BHS properties.

Richard Hyman, an independent retail consultant, said: “The Arcadia brands peaked in retail terms before [Green] bought them. Topshop until recently was doing really well but in the last couple of years it has become a shadow of what it was.

“Those businesses don’t have a proposition that cut it with the consumer enough. I think [Green] is in a real corner. He’s left it far too late.”