needing to apply for Chinese visa in London

Hi, we are currently travelling around Europe and have been away from NZ for 5 months. We wish to travel back to NZ through Asia and spend some time in China. We will be travelling to London in August - can we apply for a entry permit there to enter China in October? If so, can you give us details of where we will apply and the time it will take to get the visa. We are after a tourist visa that we will probably extend as we hope to spend 2 months in China. Thanks