By Lars Mucklejohn London fintech savings platform Flagstone has landed £108m funding from US private equity firm Estancia Capital Partners as it looks to tackle savings inertia and ramp up international expansion. Estancia is set to take a minority stake in West End-headquartered Flagstone, while its co-founder and managing director Takashi Moriuchi and vice president Keegan Mitchell will join Flagstone’s board of directors. Simon Merchant, co-founder and chief executive of Flagstone, told City A.M. that there was a “huge addressable market opportunity” in both the UK and international saving…