It hasn't been confirmed anywhere. Someone with the username 'Brightonian Belle' in the DM comments said it was in West Sussex near Zoe and that's what everyone's going off of.
That said, I really hope not. Not only is it impractical for work in London, but I feel like they'll be so isolated there with no one to spend time with but Zoe, Alfie, Poppy and Sean
. Joe always seemed very resistant of moving out to Brighton and he doesn't even seem to enjoy Alfie and co's company very much. Odd choice if this is really where they went. Maybe they're planning kids soon and want to raise the cousins near each other...