Be mindful if you do choose to go to Oslo and either check in before OR using Airportr that in the event of irrops you could be routed from OSL to your final destination avoiding LHR via DOH or HEL for example. Whilst it’s not a daily occurrence there is a thread someone of someone that went on his TP run with just the clothes on his back, his passport, iPad (?) and charger when this happen e. The ever resourceful CWS has a directory of launderettes globally for such events.
Again whilst its not been pointed out here if you choose not to do a B2B and allow a few hours this could be the worst thing to do if the aircraft for your OSL-LHR sector leaves for its outbound journey before the earlier flight. You need to have a back up plan to get to OSL.