With the prospect of warm weather ahead, drivers’ thoughts turn to convertibles. Jeremy Clarkson test-drives the new soft-tops on the market, which range from Fiat’s avant-garde Punto and the Pininfarina-styled Peugeot 306, to the Saab 900 and Toyota’s Celica GT Cabriolet. Plus Tiff Needell tries out the new 911 Turbo Porsche, the first with four-wheel drive and a turbocharger, to find out how it compares with Porsche’s classic 959 model.