The consolidation of British bank Barclays and failed investment bank Lehman Brothers could lead to a bit of subleasing activity, since it may no longer need its 24,000-square-foot office lease at the Mellon Financial Center on Brickell Avenue. Jack Lowell, managing director of Flagler Real Estate Services, leasing company of the tower, says the office is on a list of pending closures. The office lease Lehman Brothers occupied is active until 2011, he said. Lowell believes that if Barclays were to abandon its lease, he could find another tenant quickly. The building is 99 percent leased and he can be leased at $46 per square foot. Barclays’ departure would free up about 5 percent of the tower’s office space.