I'd like to see what your employer has to say about that.
Like I say it's usually a disciplinary offence not to report being overpaid.
Also paying it back over time is an administrative nightmare. Especially if it straddles 2 tax periods.
Maybe they could meet in the middle but £30 a month isn't on. That would take nearly 2 years to pay back.
I'd say bare minimum £125 a month to have it paid by march. That's minimum. Any more and it straddles another tax year.
Total nonsense in regards tax.
Its irrelevant if it covered 100 tax years as long as the employer has collected and paid the correct taxes on the remuneration that matches the periods in which they were paid.
There can be some issues on VERY large amounts clearly not paid on time which are clearly mean't to impact the revenue, but even those are very rarely progressed since its very rare that the specific date something must be paid is ever contracted.
Every year for example I can delay my annual bonus from March to April, we allow this and the revenue have no issues. Some will do so in order to change their annual tax exposure, pension contribution limits etc.
Its well publicised that when tax changes employers actually bring forwards or defer large amounts to another tax year for the benefit of their employees. You can find numerous articles in the press from the last time the highest PAYE tax rate changed.
The revenue refer to this since they can see unusual large amounts mvoing forwards or backwards as a result of the change (see tax briefing notes published on the cashflow section when these things are announced)
Its generally a contractual term to inform your employer should you KNOWINGLY be overpaid. Whether that is a disciplinary and whether the employer could make it stick very much comes down to whether the employer can prove knowingly or not.
If they can prove knowingly then then can take the defraud the employer angle. It very rarely happens as the employer is deemed to be the expert and the employee not in these cases, and as such the expert is expected to be able to deliver higher standards than the non expert.
Something you clearly shouldn't get such as say sales bonus if your shop floor, or overtime when your not allowed to nor did you claim it, can be argued to be knowingly aware if they are material enough to clearly have triggered vastly different net pay amount.
Many people will not check payslips and Ive seen a case where this was accepted as reasonable defence.
Its actually fairly normal for a payment plan to be suggested to match the amount of the overpayment. So if they over paid by £50 a month then they will deduct £50 per month.