Japan warned British Prime Minister Theresa May that her government must improve its communications about Brexit, or risk endangering inward investment in the U.K.

Days after May pulled out the stops to persuade Nissan Motor Co. to continue building cars at its plant in Sunderland, northeast England, the Japanese ambassador to London demanded regular meetings to discuss Britain's strategy for leaving the European Union.

"Of course Japan will not sit at the negotiating table when the U.K. negotiates with the EU," Koji Tsuruoka told lawmakers, including Britain's chief negotiator David Davis, at a reception in Parliament in London. "But we are friends, we are also a very major stakeholder, the Japanese economic presence in the U.K. is quite significant. Therefore this important presence will of course have an impact on how the negotiations should be conducted."