"As I've got older, I've tended to bury myself in prosthetics. I enjoy changing myself," Lindsay admits. "But Alan wrote on his script, `Fagin will certainly not have a long nose, Robert'."
Bleasdale's chief concern was to steer clear of what he calls "the perhaps accidental anti-Semitism" of the original novel. "The character is obviously territory I'm very familiar with," says the actor, "but the Fagin in the Lionel Bart musical is very different from the Fagin in Alan's script. My problem was that I had to get rid of that whole musical performance, get it right out of my head.
"Alan told me right from the start that he wanted to avoid the stereotypical Yiddish Fagin that is so prevalent in the Bart version. The whole rhythm of the language of the musical makes it like that. You can't say phrases like `Oliver, my dear' in any other way. When Alan says that he doesn't want Fagin to be Jewish, I understand completely. This Fagin is a magician from Bohemia who just happens to be Jewish. Alan doesn't want me to overplay it."
And he doesn't. Lindsay delivers a finely nuanced performance; his Fagin here - who is never directly referred to as Jewish - is magnetic without slipping into "gotta pick a pocket or two" cliches. On being introduced to Oliver, he conjures flames, multi-coloured silks and doves out of thin air before declaring with a flourish and a twinkle: "Pleased to meet you, Oliver Twist." According to Lindsay, "the fact that Fagin is foreign is beguiling and romantic to the children. He lures them to him with some kind of exotic charisma."
Some critics have suggested this spills over into child abuse. When Oliver (Sam Smith) first wakes up in the den, Lindsay's Fagin certainly has an insinuating air about him: "You see, Oliver, you're in my dreams already," he leers.
But paedophilia remains at a subtextual level - Lindsay denies playing this Fagin as an overt child molester. "There's always been this big question, hasn't there? Is he a paedophile? Well, he's not in Charles Dickens's novel." (Bleasdale may get brownie points for playing it by the book here, but purists may be less forgiving about his invention of a two-hour prologue.)
"This man has a coven of boys at his beck and call," Lindsay continues. "As kids, we've all been under the influence of some strange men. But I've made up my mind that Fagin is sexless. The big thing for Oliver is that Fagin's den is his first real home, offering food, warmth and sociability. For that boy, it must have been so welcoming after being alone for so long. To tamper with that and play up the sexual angle would be to kill Dickens."
Bleasdale, who has enjoyed a fruitful partnership with Lindsay over the last decade, echoes the actor: "Fagin is a Pied Piper, and the young children are drawn to him because of his charm and his magic tricks. I wanted to create a character who was charming and seductive without it being in any way sexual.
"There should be no ugliness about Fagin, even though he does things which we know are morally wrong. The fact is that he is an immigrant, and the laws of this country at that time refused to allow Jews to hold property. So often the only way they could make a living was either through loans or through criminal actions. This part is just perfect for Robert."
It certainly is. It plays to Lindsay's greatest strength - being attractive and repulsive in the same breath. When Fagin tells his boys with a threatening smile that "the only way to escape me is to get me hung," they can't help but find him both thrilling and frightening.
In an expressive phrase, Lindsay calls himself an "ambidextrous" performer. "Alan knows I have that duality as an actor," he says. "That's what life is like. We're all capable of that. Fagin is the ultimate chameleon; he appears one minute and disappears the next.
"As an actor, I'm never an out-and-out villain. I have a comedic side that tempts people in. Those children wouldn't stay with Fagin if he wasn't charismatic. They're at liberty to run away, but he gives them fun and a sense of wonder. At the same time, he's an extremely dangerous human being. Many times, I couldn't wait to get the costume off and wash Fagin right off me."
The same sense of ambiguity drew Lindsay towards Richard III. "One of the reasons I took the part was because I kept wondering, `how can this man win over an audience and yet simultaneously do these unbelievably awful things?'," he says. "It can only be through his complete charm. The audience have to like this guy before they can go with his story. So I made `Now is the winter of our discontent' like a stand-up comedy routine. In the language, there's a rapport between the character and the audience, which I played on."
Things have not always gone smoothly for Lindsay. After the first night of Richard III, he launched into an intemperate attack on critics - which he now regrets. "You see the critics' backs disappearing towards the exit during the curtain-call and think, `you bastards'. That first night was a nightmare, so I got up in a mood the next morning and gave it to an interviewer with both barrels. My dad rang up and said, `Why didn't you just shut up?'"
Lindsay has also been touchy about his private life since he was monstered in the tabloids over the ending of two high-profile relationships. He subsequently turned down the title role in Cracker because he didn't want the press attention.
Fortunately, over the past couple of decades Lindsay has still managed to clock up some of the finest television that money can buy - GBH, Jake's Progress and Citizen Smith, in the part that first made a star of the young Rada graduate in 1977.
All these roles have capitalised on Lindsay unquenchable, manic vitality. There are few actors better at playing Men on the Verge of a Nervous Breakdown. Even during our interview, he is overflowing with nervy energy, forever leaping up to act out an anecdote. He reckons that "we're all on that brink sometimes".
But, when all's said and done, perhaps it is this role in Oliver Twist - an intoxicating mix of the alluring and the alarming - for which Lindsay will be best remembered. He certainly seems to think so: in pride of place either side of his loo at home are two portraits of him as Fagin.
`Oliver Twist' continues on Sunday at 9pm on ITVReuse content