(Reuters) - Construction and services group Kier's shares fell 40% to their lowest level in two decades on Monday after a profit warning from the British firm, whose mounting debts also fuelled fears of a dividend cut and another funding-raising.Kier, whose stock has lost about 84% of its value over the last year, blamed higher costs and persistent pressure on its highways, utilities and housing maintenance businesses.Several big British building firms have suffered since regulators tightened..