The future of the UK listing and prospectus regime would to a large degree be dictated by whether HM Treasury and the FCA left in place the existing measures in UK law and regulation that are designed to replicate the European legislative measures that created the single market for financial services across the EU.
These include the Prospectus, Transparency and Market Abuse Directives. As the Main Market of the London Stock Exchange is a leading international listing venue and trading platform, the UK authorities may continue to require adherence to international standards equivalent to the requirements imposed by these Directives, to maintain the global reach of the Main Market brand.
Choice of market of listing is determined by a number of factors including access to potential investors, the valuation of similar companies listed on the exchange and liquidity, not solely by eligibility requirements and the level of continuing regulation and disclosure required. EU legislation only directly impacts the last two areas.
Loss of the UK's ability to participate in mutual recognition between EU Member States, as regards prospectuses and announcement requirements, is possible (in whole or in part).
Where an issuer is based outside the EU (as a UK company or financial institution would be, post–exit), an EU home Member State already has the power to approve a non-EU prospectus if it has been drawn up in accordance with international standards that are equivalent to the requirements under the Prospectus Directive. The Commission has the power to decide if a third country's law or practice is sufficient to satisfy the EU equivalence test. It could make this determination in respect of UK law and practice.