Is it possible to invest on a Motley Fool 100 based index through a UK ISA?
1I’m not sure who made the close vote but this is perfectly on topic.– VickyApr 7, 2019 at 7:30
1There is is a difference between "Questions seeking product or service recommendations are off-topic" and the question as asked. I agree with Vicky.– JTP - Apologise to Monica ♦Apr 7, 2019 at 11:53
You need to find a financial institution (i.e. a broker or a fund supermarket) that sells products derived from that index - ETFs, most likely - and that allows you to hold and stocks and shares ISA with them.
So if I were to continue from here, I guess that the next step would be to go back to the place where you found the index and ask there about which UK brokers have expressed interest on the index.