I think you will need RTK but maybe you could use a Fixed Base Station service rather than your own. I actually looked in to this a few years ago and got as far as locating the closest Leica network antenna about 5km away at a local airport. The technical details of getting this to work was way beyond my mild interest.
There are pay services used for farming and other activities.Maybe there are free ones available to you. A quick Google search of “rtk base stations uk” turned up some interesting information.
Near any of these places?
Daresbury, Inverness, Shoeburyness.
Check out this post. It’s what he is using in NZ: