Gym-goers have been promised 65 new venues by David Lloyd Leisure after a surge in 'work from club' users - despite complaints about rowdy newcomers behaving as if on Benidorm holidays.
Affluent members who pay more than £200 per month in membership fees say the discount trial offers - for as little as £20 - risk putting them off attending.
Yet David Lloyd Leisure has now revealed plans to invest £500million in 15 new clubs and 50 spa resorts as it hailed a boon in 'working from gym' regulars.
The firm says membership has reached a record high of 761,000 and highlighted the Covid-19 pandemic as a key factor, with people more motivated to improve fitness.
Yet there are concerns about the antics of new recruits tempted by cut-price temporary offers - with claims of increased thefts, assaults and intimidation.
David Lloyd Leisure has £500million plans for 65 new venues to add to its existing 133 outlets
The leisure firm's current portfolio includes this fitness centre in Chigwell, Essex
The company, which offers gyms like this, generated earnings last year of £241million
Holiday-makers are seen enjoying themselves on the beach in Benidorm, the Spanish resort which has been mentioned in comparisons regarding David Lloyd trial offer newcomers
New figures last week revealed David Lloyd Leisure now runs 133 clubs - 103 across the UK and another 30 in Europe - and had earnings last year of £241million.
The company's chairman Glenn Earlam talked up its prospect, based on a boost in membership despite the three-figure monthly fees most people are charged.
He said: 'Our business has done particularly well post-Covid. People are willing to prioritise health, fitness and wellness in a post-Covid world relatively more than they were beforehand.
'We have a lot of people that work from clubs. We have a really nice environment, separate work spaces where you can get your laptop out.
'Many people go into the office two or three days a week and during the other two or three days it’s just a bit too much being at home all the time - so they break it up and go and work in a David Lloyd club for half a day.'
But not everyone is impressed by recent experiences, with some regulars suggesting so-called 'two-weekers' making use of temporary deals were bringing venues down.
David Crutchlow, 45, told the Times he was too scared to return to his local branch in Rugby, Warwickshire, after complaining about a gang of men making too much noise in the Jacuzzi.
He claimed the men then 'pushed [him] in the changing room where there is no CCTV'.
Mr Crutchlow added: 'It's like being back at school in the changing room with the bullies. I thought, why am I paying £200 for this situation?'
Meanwhile, Oliver Newell, 27, raised concerns about his experiences at the firm's Southampton centre.
David Lloyd chairman Glenn Earlam said: 'Our business has done particularly well post-Covid'
Gym members are seen here exercising at a David Lloyd leisure centre in Leicester
He said: 'The towels go missing, the weights are never put back properly, equipment is never cleaned down. There's been damage to people's cars in the car park - theft happens.'
And another member, who uses the Gloucester branch, said the two-week deal makes the place feel 'more like a council-run leisure centre for the period of the deal'.
He added: 'Two-weekers will be walking around half-dressed, getting beers and sitting around the pool like it's Benidorm.'
A David Lloyd spokesman said: 'We do a small number of trials each year to give members the chance to share the club with their friends and family.
'Our expectations for behaviour are high, and any concerns are addressed quickly and taken seriously. We ask our members to let us know about any issues.'
The business was founded by former tennis pro David Lloyd in 1982, with the first club opening in Heston, Middlesex, that year.
It grew quickly to become, in revenue terms, the largest health, fitness and leisure business in Europe.
There were 18 clubs in the UK by 1985, at which point the company was bought by leisure giant Whitbread.
It was purchased in 2013 for £750million by private equity firm TDR, which is said to have approved the mooted new £500million investment and also co-owns supermarket giant Asda and forecourt operator EG Group.
The money will also reportedly go towards building 60 new padel courts, after a surge in interest in the sport described as a mix between tennis and squash.
A group of young women are seen on a hen weekend at a waterfront bar in Benidorm, Spain - a David Lloyd user has said newcomers are 'sitting around the pool like it's Benidorm'
This was a scene from British Fancy Dress Day in Benidorm in November 2015 - part of one of the biggest fancy dress parties in Europe and a tradition started three decades ago
During the Covid-19 pandemic, the firm held talks with the Government over potentially turning gyms into emergency field hospitals - at a time when lockdown forced leisure centres to close.
Mr Earlam also spoke out in July 2020 criticising ministers for allowing pubs and restaurants to reopen but not gyms which he described as 'the "wonder drug" of exercise that can keep Britain healthy'.
He said at the time: 'The evidence suggests that keeping the body fit and healthy could be one of the best things to do to prevent Covid-19.
'But I think gyms and leisure centres are quite far down on the pecking order of opening things up again, which seems pretty counter-intuitive.'
MailOnline has approached David Lloyd Leisure for further comment on their new investment plans and criticisms of temporary members' behaviour.