Hi Im flying from Sydney to London with a 48 hour stop in Shanghai, do I need a visa for this?

Tony, British people enjoy 72 hours free transit in Shanghai. You are eligible for 72 hours free transit. So you needn't apply in advance. Before you land at the airport, probably at least 30 minutes, you should inform the airline that you are going to apply for 72 hours free transit in Shanghai. Then your airline will inform the airport in advance. After landing, you can follow the direction boards to find the window where you can apply for it. It's for free.