Last state visit for Germany was over 20 years ago: https://en.wikipedia.org/wiki/List_of_state_visits_received_by_Elizabeth_II Angela Merkel is the longest-serving incumbent head of government in the European Union. She announced that she would not seek reelection as Chancellor in 2021.
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Parliament should debate the merits of extending an invitation to such an outstanding European leader.
Would it be a well-received honour?
Would it help cement links between the two countries?
Would it help in UK / Europe relations?
https://en.wikipedia.org/wiki/State_visit