The first version was available via the App Store, but withdrawn when the new version was due to be released.
I am not aware of any facilty to download the UK version of FTMM2 and believe you will have to buy the disk version and follow Apples instructions for installing programs on non disk drive equipped machines.
Althernatively you can buy the US version if the site will allow you to. I suspect it will not allow Canadian residents to for instance.
I think the primary differences are dictionary and the pathway into Ancestry is .com rather tham .uk, but it is the same servers/data anyway.