From 23 May 2015, London has started witnessing the phenomena of persistent twilight. This means that total darkness does not actually occur.
The implications for Muslims are related to the prayer times. If total darkness does not occur, then Esha prayer cannot enter. Furthermore, this means that Fajr time does not start.
However, as the prayers are obligatory, Esha can be prayer anytime after Maghrib, preferably late in the night, and Fajr can be prayed from the last time that it entered (about 1.20 am) until just before sunrise.