Emails linking to bogus press releases calling for Digga D's release were also sent from Scotland Yard's press bureau.
Another said: "FREE DIGGA D ON FOENEM GANG". It's not clear the artist is actually in prison now, but he has been in and out of jail in recent years.
Some of the messages were offensive, including one which said: "FUCK THE POLICE FREE THE GANG!" followed by the hashtag #CHUCKLING HELLA.
It appears hackers briefly took over UK Metropolitan Police's website, posting a series of freakish messages on its press section and social media accounts, including one which read "FUCK THE POLICE". "Cal and Dylan are gay btw", read another, apparently referring to Netflix show Tidelands.
In the early hours of Saturday, after apparently regaining control of its output, Scotland Yard said it believed the "security issue" related exclusively to the external service the Met's press bureau uses to issue news releases.
The press releases and tweets have since been removed.
The hacked account also proclaimed, without context, "XEON IS THE BEST FIGHTER IN SCOTLAND".
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More than a dozen messages have been posted so far.
Supt Roy Smith, from the Metropolitan Police, wrote on Twitter: "We are aware that the @metpoliceuk has been subject to unauthorised access and our media team are working hard to delete the messages and ensure the security of the account".
The force said it used an online provider called MyNewsDesk to issue news releases and said "unauthorised messages" appeared on its website, Twitter account and in emails sent to subscribers. We apologise to our subscribers and followers for the messages they have received.
"We have begun making changes to our access arrangements to MyNewsDesk", he added.
Met police reacted approximately 15 minutes after the attack and began deleting the hackers' tweets.
'We are assessing to establish what criminal offences have been committed'. "Please ignore any Tweets until we verify that it is back under official control".