Glen Hansard of Irish band The Frames and Czech singer and pianist Marketa Irglova starred in the surprise hit film Once, and their Albert Hall show had a similarly low-key feel at the beginning. Hansard strolled on alone and performed unplugged, more like a forlorn support act than a film‑star singer. But that didn’t last.

The Swell Season have become a big deal, thanks in large part to the curious romcom about two musicians, which won them an Oscar for best song. So far the £100,000 film has made almost £10 million and they recently recorded an appearance for The Simpsons. Oddly, there was no mention of Once during this show.

For fans of the film, it was like an alternative sequel, with four musicians in supporting roles. There was the added piquancy that Hansard and Irglova became a couple while promoting the movie, but it was their musical chemistry that kept the audience entranced.

Hansard, who had an earlier role in The Commitments, was clearly the showman in the relationship. After that quiet start, he grew into a gritty, intense performer during Lies but there was plenty of humour between songs to prevent it getting too angsty. Comparing the prestigious venue to meeting royalty, he deftly added that you a need a “healthy disrespect for a royal, especially if you’re Irish”.

He did a 20-minute solo spot and Irglova had a few songs, too. But the magic really happened when they were together, such as the heart-tugging moment when their voices intertwined on Falling Slowly, which won the Oscar.

Many of these songs appeared on their debut before Once but success has obliged them to stay on the road rather than complete their next record. One new tune, Back Broke, had the weightless quality of Nick Drake’s music and was as good as anything here.

These were undoubtedly sad, folk-tinged songs about the “muscle that’s giving you all the trouble”, as Hansard said of one heartbroken effort. But they had a joyous effect, with the audience singing along at the end, clearly overwhelmed by the emotional power of their performance.