Activity in Britain's construction sector contracted for a fourth month in a row in April as new work dried up while cost pressures remained high, an industry survey showed on Wednesday, highlighting the headwinds faced by Britain's economy. The S&P Global construction Purchasing Managers' Index edged up to 46.6 in April from 46.4 in March but remained below the 50 level that divides growth from contraction, as it has been since the start of the year.