The Brits IIRC do not use the term Top Secret. Most Secret is their term of choice.
And the Top Secret Document shown, incorrectly states that Michael Steele was a British MI5 agent when he was MI6.
I had to look that up about the “Top Secret” - below is from Wiki - changes were recently made (in 2014?)”
“Like the Protective Marking Scheme which it superseded, the GSCP classifications are applied only to the Confidentiality of the data under classification.
TOP SECRET
Information marked as TOP SECRET is that whose release is liable to cause considerable loss of life, international diplomatic incidents, or severely impact ongoing intelligence operations. Disclosure of such information is assumed to be above the threshold for Official Secrets Act prosecution.”
Not to say that alone makes this document real.