As part of the standard Permission for Commercial Operations (PfCO) issued by the CAA drone flights are not permitted at night. The CAA defines night as 30mins after sunset until 30mins before sunrise. With the submission of some additional paperwork to the CAA it is possible to vary the PfCO to include night flying. I have now received the relevant permission to carry out drone flights at night this type of flight can be a really useful and unusual way of showing off architecture and lighting schemes.
Here's an example of a recent night flight at the Moller Centre in Cambridge, the Moller Centre is located in the grounds of Churchill College.
You can watch the video in 4k on youtube.