Today there is no salt beef on view. We are in the canteen at the ITV premises on London's South Bank. Marks has with him a pile of scripts printed on pink paper. They are for the new series of Birds of a Feather, which begins shooting in October and will start on ITV just before Christmas.
They are a complementary yet contradictory pair. Marks is pale and long, Gran is tanned and round. Marks is measured and thoughtful, the fast-talking Gran has a jittery impatience about him. He is also the more cautious of the two when it comes to expressing satisfaction that they are not only back on television, but responsible for ITV's biggest comedy hit in decades. For including the repeat showings, the new Birds of a Feather is pulling in audiences of up to 12 million.
Crucially the show has kept its core characters, including Lesley Joseph as Dorien, a role that Lo and Mo, as the writers are known in the biz, based on the Jewish female denizens of a Finchley tennis club. "Expensive hair, nails, tracksuits and racquets - and more interested in the tennis coaches than the tennis," says Gran.
A third of its viewing figure would constitute a hit these days. At BBC1, which reportedly only offered the show a Christmas special, controller Danny Cohen must be kicking himself.
Yet it is only a few years since the Marks and Gran story was looking very different. "We had closed our production company and were perceived as retired," Gran recalls.
Pitching to a younger generation of executives, who were minded to turn to a younger generation of comedy writers, had become no fun at all.
"You get to the stage where you think you just don't want to go through this nonsense any more," Gran says. "But then Birds happened, largely through the theatre show [a 2012 stage version] and suddenly we were rediscovered."
"Now we are royalty, apparently," adds Marks ironically. As Gran says, "wheels turn". But some things don't change. The pair still write in what Gran, rather understatedly, calls Marks's spare room. The room is actually part of an apartment in a Sherbourne, Gloucestershire, stately home with 12 acres of land.
"For 34 years now it has been the same modus operandi," Marks says. "Maurice comes in, I stop doing whatever I'm doing and then we get on with the job."
"There is a lot of shouting and a bit of typing," Gran expands. "In the 90s, we would have six cups of coffee and produce as many scripts."
"These days we take it easier," Marks says. "We might play tennis."
"It's a very big room, you see," Gran quips.
This is the creative process that has produced much of the mainstream comedy with which generations grew up, Shine on Harvey Moon and Goodnight Sweetheart also among them. If there was an unsuccessful career period, it was their time working for Paramount in Los Angeles in 1985. It was a bruising experience. They were victims of a culture clash. They hadn't understood that producers - one of whom was Henry Winkler - expected their writers to be on hand all the time.
"We'd write 10 pages, think we can finish the script by Friday and then go out and buy a hi-fi," Gran recalls. "It was like you had jumped parole."
"One day Henry Winkler invited us to a party," Marks adds, "but I wanted to come back to England that week, which was my week off. He never spoke to us again. He ignored us. Forever."
Despite the experience, to the comedy community back in Britain Marks and Gran had been to the Holy Land, as Gran calls Hollywood - "or at least Mount Sinai".
"We were suddenly experts, not jobbing writers," Marks says. "Our careers wouldn't have been as they were had we not gone."
The shows that followed included The New Statesman, starring Rik Mayall, whose recent death at 56 shocked all who knew and watched him. "He was one of only two actor friends we ever made in this industry," Marks says.
"We had such a mutual respect because he thought we were brilliant and we thought he was brilliant," Gran adds. "It was a terrible shock."
Marks warns I should be careful about how I broach the subject of Mayall. But then the former journalist does my job for me by saying: "If you asked me, 'Did I think he was going to die'? the answer would be 'yes'."
"He lived life to the full and then some," Gran reflects. "So before the accident [Mayall crashed his quad bike in 1998] he liked to booze and smoke. After the accident he wasn't allowed to drink. But he did redouble his smoking because he had to do something naughty. He drank gallons of black coffee and he would put on a lot of weight and then run it off. He really punished the machine. It was a shame, but the bigger shame was that accident which stopped his career at its virtual peak."
If Marks and Gran are now back on top, success is not necessarily matched by critical acclaim.
And when Birds was revived by ITV earlier this year, it was given a generally snippy and negative reception by TV critics. "They never matter," says Marks dismissively.
Gran is more even-handed. "Over a whole career I would say the critics have been more than kind," he says, adding: "I always like to think that every critic has got at least one rejected comedy script at the bottom of his drawer."
Marks notes that the critics changed their tune once the viewing figures were revealed. "You can't get too out of kilter with public opinion."
Meanwhile, the duo are working on a new pilot for the BBC, which is to star Paul O'Grady, and they are in no doubt that the success of the revived Birds has made ITV think very seriously about commissioning new comedy. Will they turn to Marks and Gran?
"Almost certainly," Marks believes.
