Yeah, definitely shouldn't be used on the pavement.
The trials in Coventry have just been paused after complaints of pavement riding!
The reality is that the police aren't going to do much about it unless you're mowing down pedestrians or bouncing off cars along Red Post Hill.
Echo the comments above about locking it up - it's unlikely to survive long on the open Sheffield Stand bike racks outside ND although if there's one of those Cycle Hangers anywhere nearby, that might be worth a conversation with a resident to ask about sharing it.
Could ask TfL / Network Rail if they have any plans to install a bike parking shed or lockers at ND. Or is there anything at London Bridge? At least that'd save carrying it to/from the office. Most stations got rid of lockers (too easy to put bombs in) but LB bike parking (out the station, turn right towards the underground) seems pretty extensive and safe, it's always full of bikes and it's got CCTV. Tuck it away down there with a hefty lock around it?