Homebuilt aircraft registered in ECAC member states have always been exempt from seeking permission.
Nations which have fully implemented ECAC Recommendation INT.S/11-1 (dated 1980) - Full and free movement, no time restriction, no charge, no notification:
Austria
Belgium (added in 2017)
Denmark
Finland
France: Specified countries. Others require permission.
Germany
Ireland
Italy:
Luxembourg
Monaco: French rules apply
Netherlands
Norway
Sweden
Switzerland
United Kingdom (28 consecutive days)
Croatia
Cyprus
Romania
Slovac Republic
Slovenia