Non UK Resident doing a few days work when in the UK

Hello there, I'm in the process of completing a Self-Assessment form, and need some assistance. Prior to the tax year ending 5 April 2024, I was UK Resident with full employment in the UK. For the tax year ending 5 April 2023 I treated that year as a split-year. Having moved to Switzerland (so DTA is in place) I met all the residence tests to show that I do not need to pay an UK tax on my foreign income (I'm full time employed in Switzerland and live here full-time). I do however, visit the UK and in 2023-24 I did work on 9 days (throughout the year so odd days here and there) which were considered not-incidental (i.e. they were substantive). This was all with the agreement of my Swiss based employer and paid through the Swiss Employers Payroll. But my physical location was in the UK. Do I need to complete a the Form HS304 and try to calculate what the amount of income would be for those 9 days. As there was no UK Tax paid, I'm not completing the form to claim back any taxes and it makes no difference to the amount of tax that I either need to pay in the UK or that is owed to me (as a result of over payment of taxes on other income that is subject to UK income tax). I can understand why this form would need to be completed if my employer was UK based, but they are not. My employer is fully based in Switzerland and the work I did (in those 9 days) was part of my normal work that I could carry out in any part of the world. Happy to complete the HS304 form but I'll have to do a manual calculation of what 9 work days amounts to in Switzerland, convert from CHF to GBP, enter into the form (without any taxes being shown as no UK Tax was paid) and then say I'm exempt from this as a result of the Double Tax Agreement, which I'm not sure is relevant for this anyway. As a reminder I'm a non-UK Tax Resident meeting all the tests (to show that) and the income that had been earned was part of my full time work with my Swiss employer and paid through in the normal way through the employers Payroll in Switzerland. Many thanks for your help 

Name removed admin .

Hi,
As you were employed by your Swiss employer for those few days you worked in the UK in 2023 to 2024, you would declare this income in Switzerland and not the UK.  For this reason it does not get included in a SA100 tax return, but can be mentioned in the freehand box 19.  
HS304 is not appropriate, as this would only be completed if you had UK income from pensions, State Pensions or employments where tax is deducted at source and it is not taxable in the UK.
Thank you.

Thank you.