Secretive Switzerland-based commodities trader Glencore started laying the groundwork for a possible £21.9billion-plus flotation with the £1.4billion sale of bonds that could be converted into shares. A stock market listing would net hefty windfalls for management and employees who own the company. Glencore has close ties with Xstrata plc. Not only is it the London-listed miner’s biggest shareholder with a 36 per cent stake, but the two companies share the same chairman, Willy Strothotte, while Glencore’s chief executive Ivan Glasenberg is a non-executive director on the board of Xstrata.