Her performance in Woody Allen’s Blue Jasmine, “as a woman who finds herself penniless and on the verge of a breakdown after being betrayed by a wealthy, powerful man” was “utterly compelling” gushed the event’s host, Stephen Fry.
Cate came out on top of a competitive field that featured British stars Judi Dench and Emma Thompson.
“I was sitting in row G, so I thought that was a sign I wouldn’t be getting up,” she quipped in her acceptance speech.
But she soon turned to Hoffman, the Oscar-winning actor whose private New York funeral she attended a week ago after he died of an apparent heroin overdose.
She dedicated the award to Hoffman, hailing his “monumental talent”.
“You raised the bar, continually, so very very high and all we can do in your absence is try to raise it.
“Phil, buddy, you bastard, this is for you,” Blanchett said. “I hope you’re proud.”
The Bafta adds to the Golden Globe that Blanchett was awarded for the same performance in January.
It is speculated that the award boosts Cate’s chances of winning an Oscar as the British film awards are seen as a dry run for the Oscars which take place in Hollywood on March 2.
Doubts had been raised about the Academy’s willingness to bestow a best actress award on Allen’s film, following recent sexual abuse accusations directed at the director by his adopted daughter Dylan Farrow.
Catherine Martin has also enjoyed a successful Baftas, taking two awards on for The Great Gatsby.
Martin picked up the best costume design award and production design award along with Australian set decorator Beverley Dunn.