Sinopec has made an approach to Imperial Energy, the London-listed oil and gas explorer, which could derail takeover talks between the UK group and India's ONGC. The Chinese state-owned oil group, also known as China Petroleum & Chemical Corporation, made an approach to Imperial last week and is in the process of conducting due diligence on a formal offer. The move is the latest sign of China's ambition to buy natural resource assets and, if successful, would be the largest takeover of a UK-listed firm by a Chinese company. Imperial's assets are mostly in Russia; Sinopec has sounded out the Russian authorities about the viability of making an offer. Imperial is expected to confirm it has received a second approach when the London stock market re-opens today. Sinopec's move could scupper a