Hi mate, how far south are you? from what I can gather most people can get away with a 60cm dish for the weaker BBC channels in France although if you're on the Med then an 80cm is perhaps a better choice.
If you're not aligned to the correct satellite though, and it's critical, then you won't get a signal.
You may need to find that you have to add the BBC frequency to the Humax and then do a scan.
From memory on the humax it's something thing like
Menu
Installation
manual search
and then you can add the BBC Frequency which is:-
10773 H 22000 5/6
then try the search.. (like I say I'm going on memory, if you get stuck with tuning then say or remind me of the options and one of us will guide you through it)
if you leave the receiver on this screen without doing the search you do get a signal strength bar at the bottom of the page, this might help when it comes to aligning the dish, believe it or not I've been in the garden before with an extention lead TV and reciever trying to align my dish.. the neighbours think I'm nuts mind.. try and get yourself a cheapish sat finder if you can, saves a lot of messing about.
Remeber itv 4 and 5 are encrypted and are not available on your humax.
Hope that helps a little, despite being green with envy with you new move..
I wish you many happy adventures and good furtune in your new home..
Loop.
ps have a look here for other frequencies..
www.lyngsat.com/freetv/United-Kingdom.html