From the end of the Transition Period on 1 January 2021 and the entry into force of the Protocol on Ireland/Northern Ireland, the UK and EU produced a series of key documents regarding its (non-)implementation and indicating ways in which differences over the substance, interpretation and effects of the Protocol could be addressed. 

On 9 June 2021 the European Commission published a table comparing the effects of the EU-Switzerland Veterinary Agreement (alignment) and EU-New Zealand Veterinary Agreement (equivalence) to demonstrate their implications for EU import requirements, authorisations and prohibitions for animal products: comparison between different categories of third countries. The purpose of the exercise was to demonstrate how a EU-UK veterinary agreement could reduce checks and controls on the movement of goods between Great Britain and Northern Ireland.

On 25 June 2021 the first Annual Report of the Withdrawal Agreement Joint Committee was published covering developments in 2020. 

On 21 July 2021 the UK Government published a Command Paper entitled Northern Ireland Protocol: the way forward which outlined a series of UK proposals for amending the Protocol and the requirements for its implementation.

On 27 July 2021 the European Commission published a revised paper containing examples of flexibilities it had identified to facilitate the full implementation of the Protocol and specific 'non-papers' on the implementation of the Protocol in respect of medicines and SPS measures.

On 13 October 2021 the European Commission published four 'non-papers' setting out proposals for the implementation of the Protocol relating to customs, SPS, medicines and Northern Ireland stakeholder engagement. Accompanying the 'non-papers' the Commission published factsheets on: the benefits of the Protocol; updated examples of flexibilities and concrete examples of the potential impact of the EU proposals.

On 13 June 2022 the UK Government publish its Northern Ireland Protocol Bill which, if passed, would have disapplied elements of the Protocol in UK law and give UK Ministers sweeping powers to make law in areas previously covered by the Protocol. Explanatory Notes, an explainer and the UK Government's legal advice and justification for the new Bill were also published. 

On 15 June 2022 the European Commission published position papers on customs and SPS issues setting out more details regarding proposals made in its 'non-papers' in October 2021. 

Eventually, a set of arrangements to address most issues was agreed in the Windsor Framework which was announced by the European Commission and the UK Government on 27 February 2023. It comprised a series of declarations either adopted at the time or proposed for adoption as well as legal texts proposed for subsequent adoption either jointly in the EU-UK Joint Committee or unilaterally by the EU (for a comprehensive overview see the dedicated section of the Protocol Monitor).

On 5 April 2023 the second Annual Report of the Withdrawal Agreement Joint Committee was published covering 2021.