just in case your near portsmouth the nippon navy have three boats there, were out yesterday just off the coast firring off there guns i presume they were blanks but very lound and much smoke from them.
boats are the
JDS Kashima, JDS Shirayuki and JDS Isoyuki
Whether our forces visit a foreign country, or theirs visit ours, there is a procedure for "Diplomatic clearance" usually done via the appropriate Defence attaché and Foreign Office. The exceptions would be secret missions , but these are rare and denied if someone is caught...
We make extensive use of US military facilities as they have far more ranges etc than us. Similarly the friendly relations between our services and other countries often results in cross visits -(Difficult to do Jungle Warfare or Arctic Warfare training in Portsmouth!)