The Madrid Protocol is controlled by the World Intellectual Property Organisation (WIPO). Their website provides a list of 97 member countries that an international application can cover. These include:
United States of America
An international application must be based on an existing trade mark application or registration in one of the member countries. If you apply through the UK office, your international application must be identical to your UK trade mark application or registration. You can file your international application at the same time as you make your UK application, or later if you wish.
You can only apply for a single mark, as the international system does not allow for a series of marks (as is the case in the UK).
Read the government' guidance for more information.
European trade marks
If you have made an application for a European trade mark (EUTM) at the European Intellectual Property Office (EUIPO), or have a registered EUTM, you can use that as the basis for an international trade mark, however, you must then make the application for that mark through EUIPO.
Since 1 January 2021, UK-based representatives no longer have capacity to act before the EUIPO, with the exception of those acting in ongoing procedures (ie trade mark proceedings that were pending before the EUIPO at the end of the Brexit transition period).
Read Registering your trade mark in the EU for more information on the registration process.
UK trade marks
You can use your UK trade mark application to claim priority when applying for an international trade mark provided this is within 6 months. This means that your later application will be treated as if you applied on the same date as in the UK.
How much does it cost?
The cost to apply for an international trade mark (including an EUTM) depends which and on how many countries you want your trade mark to be protected in.
For more information on trade mark fees, read How much does a trade mark cost.