I have BUPA for myself and my 18 month old son in the UK. We move to Oz on a 176 in 3.5 weeks and have spoken to both BUPA Oz and UK about transferring our policy. In Oz BUPA have quoted me $160/month for me, my husband and my son. I currently pay £100 just for the 2 of us. They said that when we arrive in Oz, we sign up with BUPA Oz and they will essentially just bring our cover over. The beauty of staying with BUPA is that having had treatment in the last few years, these things will all continue to be covered. There may be cheaper companies out there but I would have to start all over again and certain things would be excluded. For me, it's a no brainer to continue with BUPA.
I seem to have gone slightly off track! The point I was trying to make is that if BUPA Oz can easily transfer our policy to them, surely the same could be done if you were to return to the UK.