New analysis by Cambridge and Oxford sociologists indicates that some 4.6 million people in the UK regularly experience 'precarious scheduling': flexible working with limited hours dictated by management, often with little notice, and to the detriment of employees' home lives and mental health.
Researchers say this damaging approach to flexible work is common among supermarket and care home workers, for example, with precarious scheduling affecting 3.9 million more than just those on zero hours contracts.
In fact, they describe zero hours as merely the "tip of the iceberg" of precarious employment practices - as any contract with minimal guaranteed hours subject to last minute changes and reductions offers very little security.
This can leave workers in a degrading relationship with managers: begging for schedule changes to accommodate commitments such as childcare, and competing to become management 'favourites' in the hope of additional hours - often hours originally promised to them.
Dr Alex Wood, now at Oxford University, embedded himself as a shelf-stacker at a UK supermarket while a researcher at Cambridge's Department of Sociology. He experienced first-hand the toxic interactions between shop management and the insecure - at times desperate - workers whose lives are controlled through scheduling.
Together with Cambridge collaborator Dr Brendan Burchell, Wood has now interrogated data from three rounds of the European Working Conditions Survey (EWCS) - undertaken across Europe every five years by EU agency EuroFound, most recently in 2015.
Using data from the last EWCS, the pair found that 14.7% of all surveyed UK workers routinely experienced manager-controlled alterations to their schedules - often at very short notice. They say that, when scaled up, this percentage equates to 4.6 million people experiencing some form of precarious scheduling in the UK.
The researchers' EWCS analysis is published today (16 August) in a blog post, as is Wood's latest Cambridge study of supermarket staff living with precarious scheduling, in the journal Work, Employment & Society.
"Manager-controlled flexible scheduling causes a huge amount of stress and anxiety for workers who are unable to plan their lives socially or financially as a result," says Burchell, from Cambridge's Department of Sociology.
"The practice is both toxic and endemic in many UK sectors such as care and retail. Government reviews need to look far beyond just zero hours contracts."
"The key issue is not simply the lack of any guaranteed hours. The employment contracts of millions offer little security around the hours they will be told to work in a given day, week or month, and how much notice they are given."
The EWCS data includes surveys conducted in 2005, 2010 and 2015. The recent peak of precarious scheduling in the UK was 2010, with 18.4% of those surveyed. Wood suggests that reduced unemployment since 2010 may mean slightly less pressure to take precarious and unpredictable jobs with limited hours.
"The past decade has seen a fragmenting of working time, as firms have saved costs by increasing shift flexibility through a variety of mechanisms," says Wood, now at Oxford's Internet Institute.
"These mechanisms include short and zero hour contracts, the emergence of 'gig economy' platforms, and flexible contracts that guarantee a minimum number of hours but no fixed scheduling pattern.
"Seven years of austerity have placed the public sector under pressure to contain labour costs through shift flexibility. Those who have challenging schedules imposed on them at short notice are likely to experience worse mental health, typified by anxiety and feeling low," says Wood.
During his supermarket fieldwork, Wood observed how workers were frequently expected to extend or change shifts with little or no notice - causing the majority to feel negatively about their jobs.
The latest study, out today, describes how control exerted by managers through flexible scheduling creates an environment where workers must constantly strive to maintain managers' favour.
In one London store, he witnessed managers encouraging workers to "beg them for additional hours" by making vague promises that more hours would be available.
"Staff were told 'I always have some overtime so let me know if you want any'. This was despite my entire work team being employed on less than nine hours a week and all desiring more hours or full time work," says Wood.
One UK worker, Jackie, told Wood: "It's strange because you speak to the staff and they say their department is short [of staff] but when you ask the manager they say 'there isn't any at the moment but keep putting your name down for overtime'. I'm just getting a few hours here and there."
Wood also observed managers cutting hours - affecting worker income - at short notice and altering schedules to clash with childcare and education. Some staff would often work unpaid overtime just to stay in management good books.
"Managers plead innocence, and that staffing needs are set by head office. This was frequently disbelieved. Many workers felt punished, but it was impossible for them to know for sure - adding to the insecurity," he says.