Doing this would offer the opportunity for contractors, recruitment business and clients alike to utilise UK labour.
A shining light
However, one currently shining light within the mesh of complexities associated with Brexit, is that British citizens can travel and work in Ireland without additional documentation required, due to the protection under the Common Travel Area Agreement. This might answer your question as to where is easiest to contract overseas, at least from an administrative standpoint.
As our business takes steps to provide sponsorship in the four locations listed above, we will be able to give more accurate updates. From our general research, we currently estimate that timeframes to gain Right to Work for UK nationals are between 2-3 months, with additional up-front costs of approximately €1500-€2000 using a temporary employment mechanism, the cost of which would need to be accounted for by the supply chain.