Snoop Dogg and Dr. Dre haven't performed together in the UK in 30 years -- but the two hip hop OGs broke that tradition in style last night ... and their celebrity pals were in tow.

Shaquille O'Neal and Yungblud joined forces to host the star-studded shindig inside London's Flipper's Roller Boogie Palace as Snoop, Dre -- and a surprise performance by Eminem lit up the night!!!

We're told the red carpet also extended to Idris and Sabrina Elba, Offset, Rich Paul, Dominic West, Jeremy Renner, Liberty Ross, Jimmy Iovine, Anya Taylor-Joy, Charlotte Tilbury, Jude Bellingham and Brian Grazer.

Em just released his controversial 'Death of Slim Shady' album but took it back to the classics with his unforgettable verse on "Forgot About Dre" ... and you know LeBron James rapped along with every word ... we think.

Snoop and Dre are supposed to be releasing their collaborative "Missionary" album sometime this year ... looks like they not only perfected their craft but had a bloody good time.