Tax on reinvested dividends (accumulation units)

I hold shares in an accumulating ETF (VWRP). I did not sell any shares, and did not receive any dividend payments. However, if I understand correctly, I still have to pay tax on any dividends which are automatically reinvested by the fund as explained in self-assesment-guide on the HMRC website (under UK dividends, Box 5, here: https://www.gov.uk/government/publications/self-assessment-tax-return-sa100/how-to-fill-in-your-tax-return-2022). How can I find out how many accumulation units I received? Unfortunately, this process is completely invisible to me as I don't receive any payments or extra shares. I asked my broker (Freetrade) and they informed me that they cannot provide this information for me. I tried to search on Vanguards website (the fund provider) for this information but they only provide dividend information for funds which directly pay dividends. Thanks in advance for any help!

Hi Jan Corsten,
This would be similar to an ETF and guidance is at:-
 Stamp Taxes on Shares Manual STSM101060 - Introduction to Collective Investment Schemes: Exchange Traded Fund - Overview
Thank you.

Hi and thanks for your response. This is in fact an ETF (not just similar to one). I am not sure how your link is related to the question, I don't see anything about notional dividends? How does this help me to find out how many dividends were re-invested into the specific ETF (VWRP) last tax year? I could approximate the notional dividends (using the dividends paid in the distributing sibling VWRL), but this seems sub-optimal. Many thanks.

Hi Jan Corsten,
HMRC does not hold information on how many dividends were re-invested.  
You would need to contact the fund directly for that informaiton.
Thank you