It is very tricky to recommend a lens for 'night photography' as any lens can be used for that purpose, you don't need a fast lens as you will generally need to be tripod mounted anyway. I like really long exposures (15 to 30 seconds and longer) as if someone wanders across the shot, they won't show up unless they stop moving. That means that I am often shooting at around f/8 or so. If you want people to show up in the shots, they will be blurry unless you add a touch of flash or use a fast lens at very high ISO.
Of course, blurry, ghost like figures can sometimes add to a shots atmosphere and a fast lens can help there sometimes, but isn't always necessary.
My usual night lens is also my main daytime walkaround lens, the 24-105L f/4-5.6 and both the shots below were taken with it. Your current lens selection will manage just as well at night (for shots like these) as they do in the daytime.
Really, your choice of lens depends entirely on what you are trying to achieve. Many will give an opinion on here, but they will all be for what the poster would want to shoot, not for what you want to shoot. What style do you want to do? A long shot taking in the length of the prom? Oddball angles looking up at the lights? Get a wide angle. Close-up details of the lights? Get a suitable length telephoto. Etc., etc.
If you really want a fast lens for showing people in the shot, go for a fast prime of whatever length you feel you will want most. I can recommend the EF-S 60mm f/2.8 (macro) and the EF 85mm f/1.8 I have both and they both take great night shots (as does my 300 f/2.8 ). In fact, I have 7 lenses and could recommend all of them for night work as much as for day work.
As with any lens purchasing decision, think about what, and how, you want to shoot. Think what focal length you need to translate those ideas into reality and work from there.
Good luck with the night shoots, whatever you decide to use, and maybe I'll see you at Blackpool one night, as I intend to do a shoot or two of the lights myself.

