There's nothing to stop a person who has been summoned from entering the country. Unlike an arrest warrant, the Speaker's warrant is more 'bark' without 'bite'. Because the coercive powers of Parliament are seldom used, it's unclear just where those powers derive from or how they can be practicably exercised and enforced.
As for Commonwealth countries... they have judiciaries independent* of the UK. If the subject was to visit an EU member state, the execution of a European Arrest Warrant would be a more feasible possibility, although I would think it's fairly remote (I mention it to put the Commonwealth point into perspective).
*Some Commonwealth realms (two or three, off the top of my head?) retain the Privy Council as part of their constitutional and judicial arrangements.
As for Commonwealth countries... they have judiciaries independent* of the UK. If the subject was to visit an EU member state, the execution of a European Arrest Warrant would be a more feasible possibility, although I would think it's fairly remote (I mention it to put the Commonwealth point into perspective).
*Some Commonwealth realms (two or three, off the top of my head?) retain the Privy Council as part of their constitutional and judicial arrangements.