By Lucy Raitano LONDON (Reuters) -Sterling fell to a six-day low against the dollar and euro on Tuesday with investors cautious on the British currency amid the Russia-West stand-off over Ukraine. Also weighing on the pound, Bank of England (BoE) Deputy Governor Dave Ramsden on Tuesday signalled more monetary tightening, but said he now sees a “modest” rate hike over the coming months. News on Monday evening that Russian President Vladimir Putin ordered troops into two breakaway regions of eastern Ukraine has increased geopolitical tensions and led to British PM Boris Johnson announcing fresh …