999

I was looking in the 1968 British Telecom telephone directory and I found something interesting.  On page 5 of this directory (and on page 7 of the 1965 directory), it has the following:
     Call the operator for the emergency services
                Fire
                Police
                Ambulance
                by dialling 999
                      (if available)
 (or by dialling 100 or 0 - see your dial label or dialling instructions - if the 999 service is not available from your telephone)
Tell the operator the service you want.  Give your Exchange and Number.
Wait until the Emergency Authority answers.  Then give them the address where help is needed and other necessary information.

Remember the song Revolution #9?  Reversed, it described a car crash.  And the voice kept repeating number 9, number 9, number 9 . . . .

Also, on the 1967 Beatles Christmas record  (listen at  www.youtube.com/watch?v=RPaMEHAs7nQ  ) at 3:59-4:12 it has someone speaking to the operator with the following dialog:
     Hello.  I'm speaking from a call . . . Hello, hello, operator.  Hello, operator.  I've been cut off!  I've been cut . . .   It's an emergency!!

One explanation of 999 might be that Paul and someone else tried in vain to make an emergency call on the road and was stopped by  ?

Note:  To see 999 being used, check part 5 of The Beatles' movie Help on youtube at:  www.youtube.com/watch?v=ucNbtCtfgfo at 8:03-8:12.  The Beatles are at Scotland Yard looking for help from the "chief superintendent".  The "superintendent" asks for the phone and says:  "Lifeline of the service.  Dial 999."  When Ringo says he and the other Beatles need protection, the "superintendent" says:  "And you shall have it.  Get me protection."