The UK's antitrust watchdog has joined a raft of global regulators investigating possible wrongdoing in the currency market, underscoring how the sprawling probe may have expanded in scope in recent months, according to two people familiar with the matter.

The watchdog, the Competition and Markets Authority, recently shared information concerning its own investigation into the currency market with the UK's Financial Conduct Authority, which is at the forefront of the global foreign exchange probe, the people said.