RE: Google SP11 May 2018 19:52
Peter,
Google, HL and many other sites list the closing SP at the bell which is 4.30pm UK time. However... some other sites - including LSE continue to report after the official close - thus registering late reported trades which affect the closing prices raising them upward or downward accordingly.
These late trades "will" be reported by Google, HL etc on the next trading day open though, which is why the SP sometimes suddenly either jumps or drops on open.
:-)