Some food for thought raised by Jean Heilman Grier on the impact Brexit will have on UK's participation on the GPA:
The UK’s negotiations to rejoin the GPA would involve the procurement that it would cover and the conformity of its laws with the GPA. As for its covered procurement, the UK would not be able to simply rollover its current coverage as part of the EU because elements of that coverage are tied into EU procurement directives. For example, its sub-central coverage includes contracting authorities, which are bodies governed by public law as defined by the EU procurement directive. Similarly, the UK covers contracting entities whose procurement is covered by the EU utilities directive.