Laurence Phibbs takes a long draw on his cigarette, jammed between his webbed fingers and smiles. “When my agent rang to say I’d got the part, I was jumping off the walls with excitement. Literally, and there aren’t many actors who can say that!”

We’re sitting at a quiet table in charming old school pub, not far from Laurence’s pad in South London. Well, I’m sitting and Laurence’s squatting. If any of the regulars are surprised to see a larger than normal frog sitting on a toadstool – sorry barstool – talking to a journalist, none of them are showing it.

Is Laurence a fixture here? “I hop in every now and then. It’s never very busy, so you’re unlikely to be bothered by people wanting to take a selfie or get your autograph. Although with Doctor Who, now everyone wants a high four!” He laughs and holds up the four fingered hand which expelled Jodie Whittaker’s Doctor from a mirror universe in the now-famous climactic moment of series 11 oddball It Takes You Away. “You’re kind of public property once you’ve been on the telly.”

Laurence should know. Already a familiar variegated green face from appearances on stage and screen, he’s now finally made it to Doctor Who. Laurence played the sentient universe the Solitract, which takes the form of a frog for a crucial resolution with the Doctor. Lucky for him that the universe decided to take on amphibian form. Laurence would have been out of luck if the production team had gone for, say, a talking donkey?

“They wouldn’t have gone for a donkey,” says Laurence matter of factly, whipping out his long, sticky tongue to catch an unwary passing fly. “Very difficult to dub voices over, donkeys. Their mouths are very inflexible. That’s why they’re so often CGI. Like Shrek, right? Can’t do that in studio. Though many have tried.”

Why didn’t they go for a CGI frog on Doctor Who? Laurence rolls his eyes, which is quite a feat considering they’re on opposite sides of his head. “Well, they did think about it but it’s a very emotional scene. With CG, you just can’t get the full range of emotion that a trained actor like myself can bring to a role. I mean, that’s what you’re paying for when you book me. You don’t want to embarrass an actor of Jodie Whittaker’s calibre by having her perform a scene with some shoddy imitation of a frog. You want the real thing!”

If Laurence sounds slightly arrogant about his acting chops, he can afford to be. His track record in film and TV is admirable. Roles in programs as diverse as live action versions of The Wind In the Willows and Danger Mouse have made him the go-to actor for frog roles in the UK. Is there enough work around for him? “You’d be surprised actually. I mean, wherever there’s a story with a handsome prince there’s a role for me in it, so panto’s a godsend for me. Plus I always get kissed by the princesses!” he adds, with a grin.  Is it true he’s attached to the new Kermit bio pic, Rainbow Connection? “I can’t talk about that,” he says coolly, scratching his eye with one of his hind legs.

Laurence may be the charming green face of the Solitract, but its voice belongs to Sharon D Clarke, who has played Grace throughout the season. Did Laurence mind not delivering the vocals to go along with his physical performance?

For a moment, he inflates his throat sac in bubble of what could be frustration. “Look, it was a hangover from when they were thinking of it being CG. They’d booked her and recorded it and everything, so I just said, “fine”. I mean, it’s part of the story too, but I told them I was happy to do it and of course, I said the lines on the day, to give Jodie something to work with. But they stuck with Sharon, who of course did a marvellous job, and that’s great. But I thought I brought a nice croaky quality to those lines, so I do regret it a bit. Perhaps it will turn up on a DVD extra one day.”

Take us through the day of the shoot. “Well, it was quite hilarious really. Because as you know, security is so tight on Doctor Who. They smuggled me in in the back of a car, in a shoebox which thankfully they’d remembered to punch some airholes in. Then they took me straight to make-up, where they spent a long time giving me a slightly rubbery, artificial kind of look. They were going for a slightly unreal, fantasy feel, in tune with the whole episode really. And then it was straight to the studio where Jodie was waiting. I must admit she seemed little taken aback when she saw me – overawed maybe, I don’t know – but after that initial hesitation, I thought she did very well. I gave her a few tips, cracked a few jokes to put her at ease.”

He pauses for a moment, to secrete a moisturising fluid from the glands at the back of his head. “Actually, I don’t know if I’m allowed to tell you this… but hey, what does it matter now. They were thinking about keeping me on.” What, as a regular? “Yeah, as a member of the TARDIS crew. You see, they were sort of worried that they didn’t have quite enough companions, and they were thinking of the range of stories they could tell if the Doctor had a talking frog sitting on her shoulder But the dates wouldn’t have worked out. I’m mean they shoot for six months of the year, I hibernate during winter plus I shed my skin every few weeks, so continuity would be a nightmare.” But if those logistical problems could have been ironed out, would Laurence had said yes? “I’d have jumped at the chance. I mean, I’ve loved Doctor Who ever since I was a tadpole. It would have been amazing.”

I get the sense that Laurence might be holding out for an even greater prize. Would he ever consider playing the Doctor? “Well, it’s very interesting, isn’t it?” he says, gently lifting his suction pad fingers off the stool, and bringing his hands together, contemplatively. “We’ve now got a female Doctor… why not a frog Doctor? I think it could work. Frogs naturally metamorphose anyway, so regeneration’s a doddle. Plus imagine how quickly I could out hop those Daleks! Yes, I’d certainly consider it if it ever came my way.”

Our time is up, and Laurence’s got to get to a photoshoot for National Geographic. I ask him for some final thoughts on his time on Doctor Who. “It was a hoot and I’m so pleased to have been a part of it. And who knows, maybe the Solitract’s reality isn’t entirely incompatible with the known universe and will turn up again to be Jodie Whittaker’s eternal BFF. I think she’d be delighted with that.”

He raises his hand for a trademark high four, which I happily take. Then he flies through the door with a few leaps of his powerful frog’s legs, as enigmatic as the Solitract itself. Onwards, to his next froggy theatrical triumph.

LINK TO The Horns of Nimon: the Doctor uses string to leave a path when entering into the anti-zone, a tactic famous from the tale of Theseus and the Minotaur which, the astute among you will have noticed, bears a faint resemblance to The Horns of Nimon.

NEXT TIME: The Daleks are doing something drastic in The Daleks’ Master Plan. Now will you, SHUT UP, SIR?!!!