By Sruthi Shankar (Reuters) -UK’s FTSE 100 hit three-month closing lows on Friday after Britain’s new finance minister Kwasi Kwarteng unveiled historic tax cuts and spending plans to boost the economy, but knocked market sentiment as investor concerns grew over a huge increase in borrowing. Kwarteng announced an economic agenda designed to thrust Britain out of a cycle of stagnation and into a new era of higher economic growth – but with a hefty bill attached. The internationally focussed FTSE 100 closed down 2.0% at it lowest level since June 17. The index fell as much as 2.5% to hit a six-mo…