Dining at an Italian restaurant in London with a colleague from the "Poldark" television cast, Robin Ellis was reprimanded by the owner. "What are you doing here, eating with your sworn enemy?"

A week later he was back with Angharad Rees, his "Poldark" wife, to the restaurant owner's approval: "Now that's better."

Ellis and Rees, serious young actors seasoned in the British repertory theater, are learning, happily for now at least, what it means to become character-personalities that take on life for a vast audience of dedicated TV viewers.

Here they were in Washington for the first time, on a four-city swing to do promotion spots for public television, trailing the across-the-Atlantic popularity of the swashbuckling romantic TV series of a British soldier returned to his native Cornwall from the American Revolutionary War.

For many public television viewers here, "Poldark" has picked up where "The Forsyte Saga" and "Upstairs, Downstairs" left off. And for those dreading Aug. 21, with the last episode of the current 16-part series on WETA (Channel 26), there is good news.

Ellis and Rees will fly back to England to finish filming a second 13-part series in the lives of Ross Poldark and Demelza, his wife. It will come to Washington in May.

Just why has this romantic swashbuckler captured the fancy of millions of viewers?

"It's very unneurotic," says Rees, a blond, mod embodiment of the red-haired Demelza, the scrappy miner's daughter who marries far above her station as Poldark's wife.

"Well, it's a d-good story, unpretentious, with verve," says Ellis.

As Poldark, he has been dubbed the "sexiest man on telly" in the British press, and there is evidence to support the statement as he lounges on a hotel room sofa in blue jeans and a half-unbuttoned sports shirt.

For Ellis and Rees, serious theater professionals, it has been a bit of a lark to play Ross and Demelza in a popular TV series, to spend weeks in lovely Cornwall, to ride horses, to dress up in 18th-century costumes.

Not that they don't take their television work seriously, but they still go back to the theater to "recharge their batteries."

"Ross and Demelza and the others in 'Poldark' are complicated characters." Rees adds in an afterthought in Poldark's popularity."But the story is simple, dealing with basic human values and people struggling. And the people are reacting."

At 33, Ellis has done tours with British repertory companies, played on the West End stage, and appeared with the Royal Shakespeare Company last year. He has been Edmund in "King Lear," Jack Absolute in "The Rivals," and Simon in "The Real Inspector Hound." On television, he was Franklyn Blake in the televised dramatization of "The Moonstone," the classic Wilkie Collins whodunit. He also was Essex in "Elizabeth R."

For Rees, her apprenticeship in the theater also has embraced classic and modern roles. She has been Juliet and Ophelia. She appeared with Eric Porter, the Soames of the "The Forsyte Saga," in "Man and Superman" and in the West End in John Osborne's plays.

Both Rees and Ellis aren't giving any hints about what happens in future "Poldark" episodes. When last seen, Poldark had disappeared in a hiding place below the floorboards.

"We've learned to be very cagey about giving away the plot," Ellis says.

The current series is based on four novels by Winston Graham, covering about eight years. The second series picks up the next five years and will draw from two Graham novels already published and a seventh "Poldark" novel due to be published in a few weeks.

After trips to Boston and Dallas, Rees and Ellis will fly back into 18th-century Cornwall and become Ross Poldark and Demelza. All we can be sure of is that there will be more family feuds, struggles against poverty and injustice, love requited and unrequited, gambling, fighting, bawdy fun - and an unneurotic, darn good story.