Monthly unit trust investment book cost

Hi - some 25/30 years ago I invested £100 a month in a unit trust for about 3 years. I have no paperwork from the investments made (I never considered that I would be affected by CGT at some point in the future!). Over the years I switched/transferred between various brokers so I don't have a paper trail. How do I go about working out the book cost of the investments for CGT purposes should I come to sell?

Hi sfung1973 Fung,
Sorry, we cannot advise you how you would work this out.
Thank you.