Tax Code changes - Job Expenses

A colleague received a tax code change with inflated Job Expenses which meant they received a tax refund. A month later this was corrected to Flat Rate Job Expenses £100 only which means that they now owe several hundred pounds in tax. This was not instigated by the employer or the employee. There are also other colleagues that have received a large tax refund and then had to pay it all back the following month (reasons unknown at this stage). I am just trying to find out if this has happened to anybody else and if it is a known problem for HMRC please.

Hi Maz Collins,
We would need to access the colleagues record to see what was received to put the expenses in the tax code.
Your colleague can contact HMRC  here:
Income Tax: general enquiries
Thank you.