Saturday night fever: Behind the scenes with the Strictly Come Dancing band

These people play live for up to 10 million people, week after week. Holly Williams meets the Strictly Come Dancing musicians.

The sound of six thousand people clapping in time with a tune does tend to make it go with a swing. I'm at a special filming of Strictly Come Dancing in Wembley Arena, and, as perky presenter Tess Daly and the often overwhelmed celebrity contestants keep saying, the atmosphere is "electric".

As a crowd, we're whipped up by the producers, encouraged to applaud and cheer, stamp our feet or leap to them for standing ovations. By the end of the evening my palms are tingling from all the endless clapping – clapping the judges' verdicts, clapping Brucie's rubbish jokes, clapping along to their routines – but you can see the impact it has on those on the dance floor. It's like an extra shot of adrenaline, direct into their twinkle toes. They love it.

There are 20 people in the arena, however, who do not love it. The band.

"When they start clapping along it is the worst," declares Hayley Sanderson, one of the singers in the Strictly Come Dancing house band, when I meet them. "We did the arena tour, and me and [bass player] Trev did 'Fever'. It's just me and him and finger clicks, and suddenly tens of thousands of people start doing this" – Sanderson claps her hands together like a particularly enthusiastic but clumsy performing seal – "and I'm looking at him, like, 'I can't hear anything!'."

Bassist Trevor Barry, who regular viewers of the show may recognise as the man in the hat, winces at the memory. "They clap on one and three rather than two and four… but [the producers] are trying to get the atmosphere in the studio to you at home, so you can understand it," he concludes.

Strictly Come Dancing is in its tenth series on BBC1 now, and a large part of the competition's appeal is its on-the-hoof nature – there's an extra zing to live broadcast that makes for perfect Saturday-night telly.

And the band is a crucial component: each week, they turn everything from rock songs to operatic arias to electronic pop hits into ballroom and Latin dance numbers, all live, all with remarkably little rehearsal time.

In-house bands were once the norm for television entertainment shows, but are practically an endangered species these days – and the band's presence certainly marks Strictly out from its rivals, such as Dancing on Ice or The X Factor. "It's a really massive part of the show. A lot of people don't realise [we play live]," explains singer Tommy Blaize. "It really does add something to Saturday-night entertainment. I'm not going to slag off the other side, but it is a bit of a karaoke job. I think Saturday-night entertainment should have more live bands, all over TV."

More of 'the other side' – their head-to-head rivals, ITV's The X Factor – later. But he's definitely right about the band adding something. Watching the show at Wembley, that excitement running through the crowd, nervy in case a star might be about to drop their dance partner mid-lift, is given a different kind of lift by the band being equally at risk of slipping up. As the first contestant, Lisa Reilly, sambas across the enormous dance floor, she may look like a glittery neon-orange pineapple, and the band may be playing the extremely cheesy "Car Wash", but there's a genuine little shiver up the back of the neck… It's something to do with that live buzz – and the band's music lends a sparkle that's the sonic equivalent of the thousands of sequins deployed by the costume department.

Many of them have been doing Strictly for years, and all work elsewhere as professional session musicians and singers, too. But not many professionals get to perform to audiences of up to 10 million, week after week. They all still get nervous. "Even now, when we've all got quite a lot of experience, you've got one chance to get it exactly right and your guitar or your voice or whatever is connected straight to a television and there's like 10 million people listening," begins Barry. "And that can flick into your mind, just a second before, and you go 'oh'. It makes you tense a little…"

I'm surprised they're not very tense – for many of the band, it turns out, only see the music for the first time on Saturday morning. The same Saturday that they play it in front of all those people. That's rather impressive, I suggest…

"We're all sight readers, we're all proficient at that, so it's actually not hard for us to do that," says trumpet player Simon Gardner by way of a professional breezy dismissal. But, I ask, are there any tracks which, when you come in at the crack of dawn on Saturday morning, you sit down and open up the score, make you think "Oh blimey, we're doing a –"

"Yes!" comes a resounding interruption from saxophone player Dave Bishop, to laughter from the rest of the group. "Last year I had a solo that nearly killed me, I was frightened all day. 'Five foot Two, Eyes of Blue' – it was unplayable." But at least it's democratic; everyone has their tricky numbers, everyone "gets roasted at some point", as trombonist Pete Beachill puts it. They're a jovial bunch; you sense they're all very easy in each others' company, but also supportive of whoever gets this week's fiendishly difficult part.

That said, they're not above some high jinks. Recording days are very long – the band can be in at 6am and, as I found out to my numb bum's distress, recording may go on past 11pm. When not sweating over a fiddly score, members of the band have, they confess, been known to pass the time by filling the trumpets up with water, throwing things into the tuba, and dismantling other people's trombones mid-song – although only, they're keen to point out, during rehearsals.

The band also, as the singers explain with considerable relish, get the best seats in the house; this excellent floor view of the dancers seems to help the time pass… "They do tend to come and warm up in front of us; you don't f know where to look," starts singer Lance Ellington with mock innocence. "You know exactly where to look!" counters Sanderson, saucily.

The singers have arguably a harder task than the band – there are harmonies to master and vocal styles to imitate, so they come in on the Friday night to have a run through with the rhythm section. The next day, the whole band rehearses with each dancing couple twice, then there's a dress run, and then the cameras roll. For many of the celebrities, dancing to the band comes as a shock – they rehearse all week to an edited version of a song, and while the band and singers do their very best to accurately mimic it, leaping from Beyoncé to Bryan Ferry to Shirley Bassey in two shakes of tail-feather, can lead to it sounding just a teensy bit different…

"It's difficult – say with Swan Lake, when you're trying to recreate something that's impossible with the amount of people you've got," says Sanderson. But it isn't just orchestral tracks that are problematic: newer pop songs also prove a challenge, she says, as they have "lots of effects and auto-tune. To try to sound like you've got auto-tune [on], it's quite weird." Barry suggests that, for the couples, it can be "a bit of a shock to their system: all of a sudden they've got live instruments, that aren't projected on to the floor in the way they've come to expect from the record".

All of which you'd expect to lead to slightly diva-ish behaviour… not that the band will spill on which of the dancers get precious or stroppy. "If they are divas – not that they are! – but if they're pernickety on some point it's because they've choreographed it. They're demanding on themselves, they're very passionate about what they do," says Barry generously. And anyway, should a dancer have a complaint about the tempo or the volume, the band are all able to simply pass the buck; Ellington says "we watch them march off the dance floor, sometimes they head straight to us and we all go 'that way!'" And the way they all point heads to one man: Dave Arch.

If the band are the unsung heroes of the show, he, as musical director, is its positive saint. He's very accommodating, "very forgiving!" even, about celebrity tantrums and dancer demands, the singers assure me. As well as conducting during the live shows, Arch has the mammoth task of arranging the songs; dancers will choose their tracks with the show's musical producer, and give them to Arch, who has less than a week to arrange them for the band. He estimates this takes, on average, three or four hours for each number, although it can be longer for thorny orchestral pieces, and he doesn't get much say. "I can squeal a bit, but they can usually get me to do most things," he says, with the slightly frazzled air of someone with a very busy schedule (Arch was also working on The Royal Variety Performance). "We have to find a way!"

When I ask him if they've had prima donna behaviour from celebrities, he admits "well, we have had, but it usually stems from nerves and it's normally early in the series. The first show, everyone is terrified – including us – and it's all new, there's not much rehearsal time, so then things come out."

It may ramp up the stress levels, but all of the band are adamant that having live music is important, and not just for Strictly, but for family entertainment and for the music industry itself. Sanderson – clearly not one for understatement – has a positively visceral response: "the idea of doing it with a backing track makes me feel physically sick. It's not music if people aren't all playing together – it's about personality through your instrument. And I think the guys in the band have got that!" She hoots with laughter, before adding more seriously that it would be "a massive shame" if live music stopped on TV, suggesting that these days, many people only really experience pre-recorded music.

Which leads us back to a certain rival talent contest: The X Factor. Despite being a singing competition, supposedly preparing contestants for a performing career, the hopefuls sing along to recorded backing tracks. Which, as Tommy Blaize pointed out earlier, verges on karaoke.

Barry is more strident on the topic. "Tommy said he wouldn't slag off the other programmes, but I actually would. [The X Factor] is a music show, and it's got singers, and it should have a live band. They've got more money… and people love live music. To fill it with dancers and miming musicians is a travesty." That said, it may more accurately represent the average packaged-up, plasticised pop career: during the filming of Strictly that I watch, the pop band Girls Aloud are guests, and they sing their new single to a pre-recorded musical track. While it may be industry standard, nothing better proves the band's point – compared to the live dance numbers on the night it really did feel rather flat and soulless, exhibiting a sort of chilly efficiency.

Arch is, like everyone else, insistent that live music for live telly makes a huge difference in terms of atmosphere; we're back to the crackling energy metaphors. "In the studio, it's electric really. You don't get that if you're just playing a [pre-recorded] track. Everybody is responding to everybody else. Long may it continue." Presumably, I ask him, you think there should be a bit more of live music? I mean, of course, in other shows and on other channels, but – being mid-way through another week of arranging the latest round of rumbas, foxtrots, and cha chas – Arch quips: "I think there's enough in this show!"

'Strictly Come Dancing' continues on BBC1 tonight at 6.40pm