Castle also sanctioned the construction of the Humber Bridge, which was the world's longest suspension bridge upon its opening in 1981. In late 1965, the Labour MP for nearby Kingston upon Hull North died, triggering a by-election. The marginal seat was of critical importance to the government and its loss would have reduced Labour's majority in the House of Commons to just one. Harold Wilson invoked Castle to find the necessary funding and promise the bridge's construction as an 'election sweetener'. The move paid off, with Labour holding the seat.