Returning part time after maternity leave - help

[wheresmarybloodypoppins]

Not sure if this is the right place to post but if not if you could point me in the right direction that would be great.
I’m a sales executive for an insurance broker and usually spend one or two days out of the office. Following the birth of my son I have requested to go back three days but my boss knows I will work the hours I have to on these days to get the job done. He is happy with my Request but it turns out his boss is not.
Apparently she doesn’t believe a sales role can be done part time and isn’t right for the business. I feel completely stuck and upset that I’m going to have to have a nursery raise my son all week.
Any advice on where I stand from a legal point of view? I've read the reasons they can turn down my request but not sure if their reason is valid or not?

Is anyone else in a similar role part time?

@Angrybird345 not in my team. Its a large company and I'm sure at other locations people have gone part time in a similar role.

I'd get this moved to employment matters as there's loads of knowledgeable people there.

I might be able to help as I'm in sales and I moved to 3 days a week after maternity leave. Did you submit an official flexible working request?

@OneForTheRoadThen thank you! Yes have completed the form but awaiting for the official response but managed to get the unofficial answer of the above. How does it work for you?
How do I get the post moved?

Can you arrange a job share?

Unfortunately if they believe that the role can not be done part time. And there is no history of it being done part time then that are within their rights to refuse the flexible working request.

Is there an alternative role you could transfer to?