Supported Move - can my wage follow me?

DWP staff, currently receiving London Outer pay due to location but am about to move out of the area due to family circumstances and will go to National instead. My manager is organising a supported move for me. A G7 friend who works for HMRC told me that as it's a supported move there's capacity for my London Outer wage to follow me and I simply wouldn't receive pay increases until National caught up with my London Outer pay. I spoke to my union rep about it and they said they'd never heard of such a thing because your pay is based on your location on SOP and in order to move that location would need to be changed. They said that it might be something only HMRC do.

Does this sound like something that could be possible? I've looked through guidance but can't find anything to support this idea. Obviously it would be great if it can happen, just not wanting to get my hopes up if it's not plausible.