I had a ASHP installed in a Manchester terrace last year, so it not impossible. I think you might have the 8m bit wrong, ours is certainly not 8m away from a neighbours window. From what I read at the time there are requirements for it to be "permitted development" (meaning that you don't have to get planning permission) and this includes it being at least 1m away from a boundary, https://www.planningportal.co.uk/permission/common-projects/heat-pumps/planning-permission-air-source-heat-pump . But we did have to get some of our radiators upgraded, and give up the space under the stairs for a water tank.