One of the top queries on my website is from workers who are worried that their manager or supervisor or occupational health is requesting a report from their own GP - after all there is probably a lot of confidential information in your NHS medical file. I wouldn't want anyone from work to have access to that.
No one would.
Which is why there are many protections under data protection laws and your own Doctor will be very careful that only relevant information is shared - info that can help you stay at work or even work more comfortably.
You have to give written permission and are allowed to read the report before it is sent to work (so long as you tick the right boxes on the form). If you are uncomfortable about your employer seeing the report or anything is factually wrong, consider asking your Doctor to change it. Or you can change your mind and withdraw your permission. That is totally allowed.
However, the information may be very useful to you in getting some assistance at work, especially if you have long term health issues or are struggling in your job. Your GP will be trying to help you.
So, if work asks for a report - do not be afraid, it really is to help you and not to discover anything sinister.