Barclays Chief Executive Antony Jenkins has warned of thousands of further job cuts as part of a company shake-up.In a memo to staff obtained by Sky News, Jenkins said a review to be announced on May 8th would lay out the future of Barclays, including which of its businesses it will focus on and how it will simplify the bank's operations. Jenkins said he was working on a strategy "to build a better Barclays which can deliver sustainable returns and growth over the cycle" in the wake of shareholder concerns about the bank's financial performance.The review in May will come just 16 months after Jenkins unveiled the company's so-called Transform programme to turnaround the business."Regulatory developments and the macro-economic environment are having a significant effect on some parts of our business which we need to address proactively and decisively," he said.Jenkins ruled out a full-scale retreat from the investment bank arm. He said the future for Barclays will be as a "strong, focused, international bank. And the investment bank will continue to be a part of that mix".The boss came under fire from shareholders over his cost-cutting measures and 10% rise in variable pay in 2013 to £2.4bn despite a drop in annual profits.At the time of the release of the bank's full-year results in February, Jenkins signalled about 12,000 roles would be axed across the group this year.RD