No one let me, but if you look at the back of the building it's obvious
I was scared there might be sensors or alarms guarding the roof, but obviously the bank can't envisage prospective raiders abseiling in from black helicopters, and so I didn't get caught! There'd probably be a big fuss if they'd found me up there, and perhaps I'd have branded a 'prankster' or 'mindless idiot' or something, but it was totally safe. The way I saw it, I couldn't resist seeing the view from up there... it's a beautiful scene, it's perfectly quiet and I can take night photos at my leisure without some leering drunk or scally mob trying to attack me. The nice thing about all the regeneration in the city is that these opportunities come and go, so there's often something new to try.
This one was from the top of the Unity Towers site last February. Doesn't really compare to the bank one as my camera then didn't allow long exposures...