The current size of the Conservative membership is unknown, but at the last leadership election in 2019 there were around 160,000 members, and insiders expect it to have grown, meaning the polling is not representative of the party.
Article source: https://www.huffingtonpost.co.uk/entry/liz-truss-rishi-sunak-poll-party-members_uk_62d980a3e4b0a6852c3571e4