One of the triumphs of Guy Ritchie’s reinvention of Sherlock Holmes a couple of years ago was refreshing our view of literature’s great double act in the starry form of Robert Downey Jr. with Jude Law as Dr Watson.

It’s something that the modernised adventures of the BBC series achieved too, and it says much for the appeal of Conan Doyle’s creations that it can exist with these two equally good interpretations.

“From the minute Guy got us together,” Downey says, “we cracked a book and started getting chills: ‘hey, Watson was never this chubby old dufus with his foot in a wastepaper basket. He was dynamic, he was in the army. And Holmes never wore a deerstalker hat.’ We had a chance to, not rewrite the history of Holmes, but to extrapolate from the untapped actual history.”

“You can compare Holmes and Watson to the great Shakespearean characters in a way,” adds Law. “They’ve been played by hundreds of actors over the years, and each one is a different interpretation. This is ours.”

Which is clearly evident in Sherlock Holmes: A Game of Shadows, a film that ramps up the action, and maintains the Holmesian atmosphere while also developing a story about a global conspiracy pushing the great powers towards a World War.

And a big part of the appeal is the chemistry between the two leads, a bickering relationship that rings true and reflects moments of comedy as well as drama. But don’t call it a bromance, whatever you do.

“Jude doesn’t like it when you say bromance,” says Downey gravely.

“I think it belittles it,” nods Law, then with a note of mock indignation: “it’s more than that!”

“People talk about chemistry,” Downey continues, “but what does that really mean? We were just having lunch trying to figure it out, and we’re really grateful it comes across that way. We work really hard, and we have respect for each other. Certain of us have been in sequels that sucked, and we wanted to try and avoid those pitfalls.”

One strength that this decidedly unsucky sequel can boast is a familiarity with this version of the Holmes canon, so just as the cast rejoined the adventure as friends from the first film so audiences come to it knowing what to expect. And the most pleasing thing of all is that it does not disappoint, and in fact delivers more than we could have hoped.

“We never assumed we were going to make a second film,” says Law, “but there was a lot of energy carried from the first film into this. And certainly a lot of enthusiasm for relationships that worked, that we wanted to flesh out a little more.”

Whenever anyone was in doubt about where to go with this film there was always the source material that inspired it. Conan Doyle may not get a screenwriting credit, but his spirit remains intact and burns brightly in Ritchie’s tale.

“I think one of the reasons these characters have survived the test of time, and have been explored by so many actors is because they’re incredibly rich,” notes Law.

“So first of all we had a tome of work we can lean back on by Conan Doyle, to investigate how best to keep these characters rich and alive. We’re also in a creative environment where we’re allowed to play and to keep stretching and trying new ideas within the characters and within their relationship.

“I think also, the truth is, the reason they’ve been so popular for so long is that they’re symbolic in a way of characters that we all know and that we all have in us.”

Bromance or not, when the dust settles on all the action and Holmes and Watson have – maybe – saved the day once more, there is still a playful air to the on-screen friendship between these two timeless characters that, to the modern eye, appears almost homo-erotic in nature. So what do the actors make of this interpretation?

“You mean onscreen,” Downey asks, mischievously.

“What happens in our private lives is another matter entirely. Jude and I have decided to save Warner Brothers’ money. We’ve been sharing a suite during the entirety of the press junket. We asked for a small room. With a single bed. We prefer two sinks so we can wash up before and after our nuptials. As for wearing each other’s clothes to please each other, that’s something we’re going to save for the next instalment –Sherlock Holmes – A Game of Trannies.”

Cue much laughter, and an invitation for Jude Law to respond. Still laughing he shrugs: “How can I follow that?”

The magic remains, the game’s afoot and the series may yet continue.