Terryl
Over "here" (and the rest of Europe), manufacturers must meet relevant EU Directives (specifically the RTTE now and the RED in future) and that means they must meet specific ("ETSI") standards for the emissions, immunity, spectrum usage and so-on requirements, and there are specific emissions limits for WiFi devices - provided that the manufacturers declare on their "Declaration of Conformity" mentioning the standards applied, stick the "CE" marking on the product (and have all the test data and so on to back that up) then they can self-declare and market the product anywhere in the EU (although I seem to remember that they do need to register with the authorities that they are marketing that type of device).
There are, AFAIK, no relaxations for "difficult" environments, and would you have to apply for a specific (probably very difficult to get!) site licence to use any form of "booster" - don't forget that most of us live in far more crowded environments and our neighbours are often feet/ yards away and not, as in your case, miles, and so interference between properties has to be avoided/minimised (otherwise most of us would probably not be here on this forum as we would not be able to send/receive unless cabled Ethernet were used, and most domestic buildings don't have that - but mine does!
)!
We don't allow boosters on CB either - although undoubtedly some "miscreants" do use them
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