British chemicals and sustainable technologies firm Johnson Matthey Plc said on Wednesday that it plans to buy back £250 million ($317 million) in shares. The maximum number of shares that may be repurchased is 18.345 million shares with an aim to reduce the share capital of the company. Under the first tranche of the repurchase, the company will commence repurchase of £125 million of shares with immediate effect. Johnson Matthey has entered into a deal with Citigroup Global Markets Limited to purchase the shares for subsequent repurchase by Johnson Matthey. All shares repurchased under the dr…