Brexit will not affect the Interrail Pass
If you're a UK citizen, you can still travel with an Interrail Pass – this won't change as a result of the Brexit. Check the UK Government advice on how Brexit will affect travel to the EU.
Citizens of European countries that are not members of the EU, like Switzerland and Turkey, can also travel with an Interrail Pass. Interrail travellers from outside the UK will continue to be able to use their Interrail Pass to travel in the UK, too.