Mumbai, Sept. 2 -- British pound tumbled around 1% against the dollar as UK's 30-year gilt climbed to their highest level in nearly 3 decades. UK's thirty-year gilt yields touched a peak of 5.680%, up about four basis points on the day, their highest since May 1998 over concerns of a widening UK budget deficit due to UK Chancellor Rachel Reeves' decision to increase borrowing in last year's budget, in turn increasing the "risk premium" on longer-term gilts because of uncertainty over its rising debts. GBPUSD is quoting at $1.3379, down 1% on the day. Meanwhile, downside in pound and euro over rising fiscal concerns is seen supporting gains in the dollar index that measures the greenback against a basket of currencies in which the two curr...