Shares in travel firm Thomas Cook plummeted Tuesday morning after the firm said it was in talks with its banks about borrowing more money.This was due to a "deterioration of trading in some areas of the business in the current quarter", the firm said.It added that it would delay the release of its full year results until the discussions were finished.In October, Thomas Cook said aid it had reached agreement with bankers to amend the terms of its existing facilities while securing an extra £100m of headroom. Shares fell 51% on opening. Before today the stock had dropped 78% already this year.