They’re most known to have come from the UK, but Australia had 1999-2000 English booster packs as well (as already mentioned by @cwebfan23); Poland had them as well, usually with a Polish sticker on the back (including ‘Made in U.K.’):
And even the USA had a very brief 1999-2000 release.
More info about all the Base Set booster packs can be found in this excellent article thread:
Greetz, Quuador
