Leader: The decision Gordon Brown makes on whether to proceed with Britain’s first new coal power station in two decades will make or break his environmental reputation. It will either confirm the Prime Minister’s claims to be a leader in the struggle against climate change, or expose him as an imposter. The owner of the Kingsnorth power station in Kent, E.on UK, wants to replace the existing plant with two new coal units by 2012. According to the company’s chief executive, these units will …