By Shashank Nayar and Ambar Warrick (Reuters) -Britain’s midcap stock index slumped to a 10-month low on Monday as rising concerns over Russia and Ukraine rattled global equities, while reports of dealmaking activity helped Unilever and Vodafone outperform. The domestically focused mid-cap index tumbled 3.6% to its lowest since March 2021, while the blue-chip FTSE 100 index fell 2.6% to a one-month low. Most sectors were in the red, as the tension between Russia and the West, along with anticipation of major central bank meetings this week prompted losses across global markets. Unilever jumped…