Have I just lost a lot of money in tax?

[draxdomax]

For the previous tax year, I joined a new employer as a PAYE and received a 5000 sign-up bonus.
I actually received about 2500, due to tax, which has been fully calculated and paid for already for the whole year (22-23).

This tax year, I am leaving them because that company is terrible to work for.
However, my contract stipulates that I must refund the sign-up bonus, pro-rata for how long I've been with the company.

Had I stayed with them for a whole year, the entire bonus would have been mine
to keep.
Since I am leaving at about 6 months in, I would have to return about a half of the bonus, let's say 2500.

So, what happens with the tax I paid 22-23? Can I tell HMRC to rewind that year and not count my 5000 as 5000, more like 2500?
I know there's a legal precedent that HMRC do not respect this particular situation (someone had a similar case to mine, albeit their sign-up bonus was like 150,000... And HMRC didn't refund him anything).

Hopefully someone with tax calculation skills can tell me:
Assuming I don't get anywhere with HMRC, would the fact that I am returning money to the employer somehow result in "less tax" for me this year and therefore no financial loss (from the point of view of those two years together)?

For what it's worth, I received about 120,000 for 22-23 and expect to earn about the same for this tax year.

Any thoughts, ideas, discussions welcome :)

@draxdomax I would expect the refund to be processed via PAYE so you would receive a tax refund as your gross pay would be less.

This page is relevant to your situation:
https://www.gov.uk/hmrc-internal-manuals/employment-income-manual/eim00810

@WuTangGran yeah, that's the case law I was referring to in the original post.
If someone worth 147,000 (as a sign-up
bonus!) Couldn't figure it out with HMRC, I am not hoping for anything like that.
Probably shouldn't have even mentioned it.

As Tipping said above, can they recover it via your last salary payment? How are they proposing that you refund it? Deducting from your final salary would make sense, balance off any tax paid and probably NI too.

The decision shows you can offset the amount repaid against current year earnings:

“Judge Warren then applied that analysis to the particular circumstances of Mr Martin’s case and concluded, on his interpretation of the relevant clauses in the employment contract, that the amount paid by Mr Martin should be taken into account as negative taxable earnings.”

Yep they should deduct from your salary so in effect giving you the tax back.