The investment banking business of Barclays is preparing to sack several hundred staff in reaction to a sharp downturn in activity during the second quarter.Back office and administration jobs at Barclays Capital (BarCap) are most likely to disappear, people close to the action have said.Numbers at the unit, which has a big presence on Wall Street following its purchase of Lehman Brothers' American business in 2008, have ballooned by almost 20% in the last year to over 25,000.There was a 16% decline in fixed income, currencies and commodities business from the first quarter to the second, and a 17% drop in investment banking, results revealed last week.BarCap's aggressive expansion under Bob Diamond's leadership could now be called into question.