British people travelling to the European Union will have to pay €7 for visa-free travel from 2021.

The post-Brexit move was confirmed by the European Commission in response to a question to its President Jean Claude-Juncker.

Alongside the fee, UK citizens will also need to pre-register for the three-year electronic visa waiver - similar to the ESTA visa system in place for Irish people travelling to the US.

The small print of the detailed draft regulation covering visa exemptions for UK citizens travelling to the bloc says that "the European Travel Information and Authorisation System (ETIAS) will apply to United Kingdom nationals once union law on free movement of union citizens ceases to apply to them, as to other visa-free third country nationals".

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The maintenance of visa-free travel for short-term visits to the EU, and by all EU citizens to the UK, has been heralded by the British government and Prime Minister Theresa May as one of the great achievements of the political declaration agreed by EU leaders at the special summit last month.

Sky News reports the EU has already begun to implement the system, which pre-authorises the entry of citizens from a special list of countries, who do not require full visas.

"Once ETIAS enters into operation, all visa-exempt non-EU nationals who plan to travel to the Schengen area will have to apply via ETIAS," a European Commission source said.

The change might be put off if the transition period is extended and EU laws on freedom of movement continue to apply to the UK.

The charge is unlikely to be applicable between Ireland and the UK, as this is covered by the Common Travel Area and is outside the Schengen zone.