The PM likes to go there, plans are made to assassinate him en route.
“Assassination is the sincerest form of flattery.”
The Ministry of Defence has Special Services Section (SSS) for that.
“Just suppose the Channel Tunnel were built, how would you go about flooding it?”
The similarities to Executive Action (dir. David Miller) and The Domino Principle (dir. Stanley Kramer) are striking, though the main basis is the attempt on De Gaulle in 1962 at Petit-Clamart.