What is the Withdrawal Agreement and who will benefit from it after the end of the transition period in terms of residency?
The Withdrawal Agreement is a legal document that provides a legal and political framework on some aspects of the separation between the UK and the EU (such as residency rights and a protocol on the Irish border) and contains a political declaration about the expected future relationship.
On the residency aspect, it is stated that UK nationals must be lawfully residing in Spain before the end of the transition period to benefit from the provisions of the Withdrawal Agreement regarding residency rights. By "lawfully residing", it means UK nationals that can provide factual proof they lived in Spain before the end of 2020 when applying for residency.
UK nationals coming to Spain from 1 January 2021 onwards will have to apply for residency through the General Immigration Regime, which involves a visa application.