2× Participating Liquidation Preference
Investors get 2× their money back AND share in the rest with common shareholders. On an £8M raise, that's £16M off the top before founders see anything.
On a £40M sale, investors take £16M (their 2×) plus their pro-rata share of the remaining £24M (~£4.8M). Founders end up with about half of what their cap-table % implies.
Push for 1× non-participating as the baseline (market standard). If they push back, accept 1× participating with a hard 2× cap.
"1× non-participating, with no double-dip on liquidation events."