Comet C/2016 R2 (PANSTARRS) is forecast to reach its brightest, at around mag 11.3. It will lie at a distance of 2.93 AU from the Sun, and at a distance of 2.06 AU from the Earth.
From London, it will be visible in the evening sky, off the nose of Taurus, becoming accessible at around 17:28 (GMT) as the dusk sky fades, 27° above your eastern horizon. It will then reach its highest point in the sky at 21:38, 52° above your southern horizon. It will continue to be observable until around 02:12, when it sinks to 25° above your western horizon.
Doug.