I would say that legally you almost certainly won't have a case unless you can prove discrimination (based on age, race, religion etc). From your description it sounds like the set up of your company means that your employer could justify treating you differently to others, even of the same grade or job-title, due to being in a different location.
Of course this doesn't mean it's fair for them to operate like this. If you think they value you enough to want to retain you I would recommend having an off the record conversation with a line manager to put down a marker and get a feel for whether they are receptive to compensating you as they have other teams. From experience I would avoid going down the HR route at this stage as they will be by the book and are unlikely to be the ones making a decision.