SIPPING TEA face to face with the Kemp brothers, after seeing them as diabolical gangsters in the British movie "The Krays," is a little unnerving at first. But Gary Kemp, the black-haired, more psychotic half of the screen twins (see review on Page 53), is fair-haired and softspoken, and about the only thing Martin Kemp pulls on you is a ready smile.

They're brothers, not twins; dads and husbands, not gangster killers. They're also the heart of the technopop group, Spandau Ballet, but, they hasten to add, they are also actors. Before 10 years of MTV-era music, there were 10 years of drama school.

Because of this dramatic experience and the sibling connection, they were approached for the parts and snapped up the offer, putting the music on temporary hold.

"It had to be {real} brothers" playing the title role, maintains Martin, 28. "There are certain things that brothers do. We felt, when we were filming, that we could take it a stage further than you would with actors."

In a scene in which the Kray brothers take each other on in the boxing ring, for instance, "we'd hit each other harder, full contact, where you wouldn't do that with other actors."

"It was a matter of discovering the mutual, subconscious quality of our relationship," adds Gary, 30. "Because we needed to have an even stronger one as the twins . . .

"Emotionally, we had a truth we could believe in. It gave us a basis. You know when you're studying for your character, you do a lot of self-analysis. Because there was a third character in the movie -- the twins -- we had to do a lot of analysis of our own relationship."

And what did they find out about each other?

"I don't like him," says Martin, "and he don't like me."