The long-hours culture in too many workplaces is holding back the economy, a Coalition government minister has warned, as every worker gets the right to ask for flexible working from today onwards.
Business Minister Jo Swinson suggests some office staff may have their jacket "on the back of the chair" at work, but they are achieving little and even wasting their time surfing the net.
But business leaders have warned that today's widespread changes will increase costs and red tape for employers and even lead to resentment between co-workers.
Previously only about half of workers, mainly parents, have had the right under law to ask for flexible working.
Now all staff, about 20 million people across the UK, can ask for a vast array of arrangements including different hours or working from home.
Employers will only have a duty to consider requests that are reasonable.
But a new survey published today suggests many companies are unaware of the changes - despite their potential impact.
Recruitment site Jobsite found nearly half, 47%, of Glaswegian businesses admit they are not prepared.
Ms Swinson, who also returns to work today after maternity leave with her first child, said a culture change was necessary in many workplaces.
"I think there is still a kind of throwback, where we still have a 'presenteeism', long-hours culture," she said.
"Where it is about whether or not your jacket is on the back of the chair. [About] whether you are sending an email at half past eight at night ... I think [that culture] is actually quite damaging."
She added: "What what matters is results.
"It is about whether you do the job that you are paid to do and whether you are effective at that job, rather than about the number of hours that you actually devote to it."
The bigger issue, she warns, is not just for individual workers or individual workplaces, but for the economy as a whole.
"Getting rid of presenteeism culture will be a very healthy change and actually good for productivity and for Britain's economic growth.
"Getting a stronger economy so that we can have good jobs, good-quality jobs and people in work that they find meaningful and enjoyable".
She also suggested there were offices where people were putting in long hours, not necessarily on the day job.
"The internet can be a wonderful thing in many ways, but it can provide a distraction", she said.
And she said that extending the right to ask for flexible working to all workers would also break down the "tensions" in some workplaces around the perception that parents were getting a better deal.
But Kim Pattullo head of employment law at HBJ Gateley, which has offices in Edinburgh and Glasgow, warned that might be a rose-tinted outlook.
"There's sound logic in giving people the opportunity to shape their working lives around other things, but for employers there could be a serious storm brewing," she said.
"If a few people in a small team come forward at the same time, how do you make that decision, balance your commitments as a business, and then try to keep everyone happy?"
She also warned that too few Scottish employers were aware of the change and many would not be ready for the introduction of the legislation.
Business leaders have criticised the extended rights, saying they will harm productivity.
Adam Marshall, director of policy at the British Chambers of Commerce, said: "The new rules make it harder for employers to prioritise requests."
But TUC general secretary Frances O'Grady warned: "Employers will still find it all too easy to block any requests for greater flexibility."