Image copyright Melissa Brooker Image caption Melissa Brooker and her daughter, Isabelle, now aged five

Melissa Brooker had been in her job as a senior HR director for 10 years and "loved every minute of it".

Then she had her first child.

"Sadly, the year I returned took the shine off for me," she says. "Gradually, it became obvious that my employers still needed a lot of face-time. I could see that I was going to be left out of key meetings and opportunities by rigidly sticking to the hours I was paid for."

So she tried to find a way around it. "I accepted meetings and calls on my days off. I dialled into calls while my baby was asleep, praying she wouldn't wake up.

"I worked in any snatched moments I could find. No matter what your hours, there was an expectation that if you wanted to progress, you had to be 'always on'. It just wasn't sustainable."

"Sarah" also works in HR. She doesn't want to use her real name because she's worried about losing her job.

Although she loves what she does, she says, "The isolation I have felt at work since going part-time shocked me, and has been soul destroying. I feel punished for not being there five days a week."

'Tough cookie'

This is not the way the flexible workplace is supposed to be. Since 2014, the law has been that any worker has the right to apply to work flexibly.

It's no surprise Sarah and Melissa's stories are so similar.

Image copyright Melissa Brooker Image caption Melissa Brooker and her second child, Ethan - she has since quit her job and set up on her own

A survey by flexible working experts, Timewise, found two-thirds of part-time workers feel isolated and struggle to make professional connections.

Sarah returned to work after a longer gap than usual having had two children close together. "I'm a tough cookie, believe you me, but there have been occasions when I have cried. Friendships I have built over five years have simply dissolved."

As flexible working is the way most of us now work in the UK, this is a major problem.

'Flexism'

Timewise's report, Part-time Work: The Exclusion Zone?, found:

Nearly seven in 10 (68%) feel so grateful to be allowed to work part-time that they accept career compromises

feel so grateful to be allowed to work part-time that they accept career compromises More than half (59%) miss out on networking opportunities because they conflict with their own working patterns

miss out on networking opportunities because they conflict with their own working patterns Two-thirds (65%) feel less connected to their own teams because social events are harder to make

feel less connected to their own teams because social events are harder to make More than half (59%) feel they have fallen behind full-time colleagues in terms of skills and knowledge.

Timewise founder Karen Mattison calls it another form of discrimination: "flexism".

"Much of working culture is still rooted in the five-day 1950s model, with a lack of flexibility around when meetings, training and networking take place - leaving part-time workers isolated.

Image copyright Timewise Image caption Karen Mattison: "Part-time and flexible aren't the future of work. They are the now."

"As few as 6% of people are thought to work a traditional '9 to 5', we have a strong mandate for change.

"Part-time and flexible aren't the future of work. They are the now. And they are the way most people want to work."

A recent survey for accounting body Cima found flexible working came top of the list for two-thirds of respondents, above even pay.

'Strategic tool'

Timewise is calling on businesses to do more to harness the potential of their part-time employees by taking a more proactive approach.

The organisation is launching the PowerFlex Network - the UK's first cross-business network to support middle and senior management part-time and flexible workers.

It plans to offer networking opportunities, speakers and training, in order to help those working part-time and flexibly who are currently missing out on the opportunities that their full-time colleagues take for granted.

Media playback is unsupported on your device Media caption When working part-time isn't viable

Claire McCartney from the Chartered Institute of Personnel and Development (CIPD) says that, used sensibly, flexible working brings great benefits.

"Flexible working can be used as a strategic tool to support improved individual and organisation performance through developing greater diversity, brand competitiveness and increasing levels of job satisfaction and commitment from workers."

But she adds that in order for this to happen it is "extremely important that they receive the same opportunities as those that work more traditional patterns, when it comes to skills development and progression".

Flexible working and the law

In April 2003, the government introduced the "right to request flexible working"

This applied to parents and certain other carers

In 2014 this was extended to include all employees with at least 26 weeks' continuous employment, regardless of parental or caring responsibilities

Employers have a duty to consider a request in a reasonable manner and can only refuse a request for flexible working if they can show that one of a specific number of grounds apply

The advisory service Acas has issued guidance and a Code of Practice for employers on handling such requests in a reasonable manner

Source: CIPD

Image copyright Getty Images Image caption Many part-time employees report feeling isolated at work

Leading companies, including EY, Lloyds Banking Group, Dixons Carphone and Diageo back Timewise and its work.

Lloyds has made some major changes. In the last two years it has increased the proportion of new roles with agile working arrangements from less than 10% to over 90%.

Assad Malic from Dixons Carphone says it is looking at getting rid of standard contracts entirely.

"We have an ambition to remove the standard 37-hour, 9am to 5pm contract altogether over the coming years and we go to every effort to make our flexible and part-timers' experience feel inclusive and progressive," he says.

'No choice'

The lack of acceptance of her way of working caused Melissa Brooker to leave her job and set up on her own. She now works how she wants, and no-one seems to mind.

"The fascinating thing is that since I've become independent, clients aren't at all fussed about the hours I work. If I need to say, 'I can't work past 3pm,' they are always fine about it. I miss being part of a team but this has been my solution and it has worked brilliantly for me."

Meanwhile, "Sarah" is stuck with her unhappy work life. "I have to stick it out. I have no choice. After 11 years at this level where else can I go?

"In any case, I have actually been for a few job interviews and I was told I had to work full-time, there was no other option."

Looks like Timewise will have plenty to keep it occupied in changing the working landscape for people like Sarah.