Tom Jones, Union Chapel, London and Jonsi, Dome, Brighton

Even more gothic-looking than usual, the octagonal interior of the Union Chapel is tonight choked by a fog of smoke, the arches behind the pulpit lit a sepulchral shade of blue, switching to a demonic red the very moment Tom Jones takes to the stage. "Beautiful venue," he acknowledges after the opening "What Good Am I?", glancing around the packed pews. "Very fitting for the album ..."

A deconsecrated church? Indeed it is. Praise and Blame is the septuagenarian's back-to-roots foray down the now well-trodden Johnny Cash route: his "Welsh Recordings", if you wish. Consisting of aeons-old gospel, folk and blues songs by the likes of John Lee Hooker, Bob Dylan, Billy Joe Shaver and the ever-prolific "Trad", it's predominantly religious, or at least haunted by angels and demons, pride and guilt. "If you take the praise," he says tonight by way of explanation, "you've got to take the blame. People say 'Tom, he's got a lovely voice ... but he's a bit of a naughty boy.' You see?"

We see. Indeed, the well-documented misdemeanours of Tom Jones – satin-shirted satyr, serial shagger – are part of his appeal: charming the panties off the universal female, and giving her one for us. There's none of that hip-grinding sauce tonight, however, as the increasingly King Neptune-like Jones takes us through Praise and Blame, start to finish. He's on fine form vocally, and he's funny with it, contradicting one heckler by clarifying that the Vocalzone lozenge he pops in his mouth is not Viagra, and name-dropping "my good friend" Elvis Presley before a sweaty-browed rendition of "Run On", the song the pair used to sing in the Vegas years of the early Seventies.

It's impressively raw, tough-arsed, hard-knuckled blues-rock fare. "Nobody's Fault But Mine" would work in a particularly gritty Lynch/Tarantino/Coens scene, and the line "Lord, help the motherless children" in Jessie Mae Hemphill's delta blues standard almost works as a hip-hop cuss.

We sit politely, in anticipation of a hits encore. A publicist tells me that the single most frequently asked question she's fielded all day has been "Is he gonna play 'Sex Bomb'?", but I'd have settled for "Green Green Grass of Home" if he doesn't want to disrespect the surroundings with something so sleazily secular. Instead, we get the happy-clappy "Didn't It Rain" for the second time in one night.

There's been plenty to praise, but if anyone shuffles out of the aisles feeling a little let down, there's only one man to blame.

At the scene of Abba's 1974 Eurovision victory, a quiet triumph is scored by an altogether different type of Nordic pop star. Blind in one eye, vegan, elfin, openly gay but somehow asexual, with a voice like a 19th- century castrato (a rare recording of one, non-coincidentally, appears on his "Boy 1904"), Sigur Ros frontman, Jon "Jonsi" Birgisson, cuts an unconventional – and very slender – figure: I know at least one aficionado who believes he's a fairy (in the supernatural, not the sexual sense). But that's Sigur Ros fans for you.

While the rest of the Reykjavik band are taking an "indefinite hiatus" to breed, Birgisson has been busy, first recording the instrumental album Riceboy Sleeps with boyfriend Alex Somers (who plays guitar and gadgets in his touring band), then with this year's Go, which breaks with Sigur Ros tradition by featuring vocals sung in English, as opposed to Jonsi's invented language Vonlenska (or "Hopelandic") or, on songs like "Animal Arithmetic", switches between English and his native Icelandic.

The prospect of a Jonsi solo show might appear somewhat dry, given that he specialises in intricately pretty but essentially ambient sound. It's fortunate, then, that he's seen fit to present it with a multimedia or "cross-form" extravaganza which verges on the epic, courtesy of theatrical team 59 Productions and composer Nico Muhly, encompassing film, art and animation. What this means in practice is visuals that suggest the rage of nature at its most biblical and its most gentle, echoing Jonsi's elemental lyrical lexicon of volcanos, wolves and forests, as well as some startling feather head-dresses. And if you want to see glockenspiels played with violin bows, Birgisson's your man.

The singer, described by The New York Times as "a messenger of ecstatic hope" exerts a powerful grip over his throng. On the single "Go Do", people stomp and clap like they're wearing Agnetha Fältskog's blue satin knickerbockers, but more often they're rapt and motionless. During songs such as "Tornado" ("I wonder if I'm allowed just ever to be ...") and "Grow Till Tall", on which he holds a note for so long it seems to blend into the underlying synthesiser and it's impossible to know where one begins and the other ends, people around me are welling up.

It isn't always possible to divine whether they're the tears of the emotionally transported, or tears of boredom. It barely matters: either way, your face still gets wet.

Next week

Five years on from the singer's cerebral haemorrhage, Simon checks on the health of Edwyn Collins