When Maddy Prior told her mother “We were going electric,” she replied “What are you going to do with the gas cooker dear?” Maddy’s smile lights up her face like the seaside illuminations in her Blackpool birthplace. The singer had been talking about her folk-rock band Steeleye Span, of course, rather than her new kitchen. But even she wasn’t expecting them to appear on Top Of The Pops three years later. Steeleye Span’s ethereal rendition of Gaudete, a half-forgotten 16^th century Christmas carol, soared into the charts in December, 1973, surprising everyone – including the band. For starters it was the first, and so far the only British chart hit sung entirely in Latin, and secondly it had flopped the year before. Their record label Chrysalis re-released it without consulting them. “I don’t know why they saw it as a single, we thought it was unlikely to be a hit; the recording engineer hated it,” Maddy tells me. “When we got on Top Of The Pops, we couldn’t believe our luck. It was the only music show on primetime TV back then. We wanted to sing, but they said we had to mime. So we walked about holding candles. “We were just laughing all the time. We thought it was incredibly funny.” Slade were on the same edition with their own Christmas perennial, Merry Xmas Everybody, and Wizzard weren’t far behind. “It was great because it wasn’t where we were heading, but it just sort of happened.”

The folk-rockers went Top Ten two years later with All Around My Hat – an early 19^th Century ditty about a Cockney costermonger whose light-fingered beloved had been transported to Australia. Then Chrysalis released Hard Times Of Old England. “They thought it’d be relevant to the times – it’s relevant all the time!” says Maddy, 78.

Her voice is so soulful that a New York producer who heard their track playing asked, “Is that the new Etta James album?” But the only things Steeleye Span took from America were their Fender guitars. Fame came by accident. “We were always more interested in the music. We wanted it to be popular and not overly esoteric.” Maddy started singing aged nine with the Blackpool Co-op Choir. Then the family left Lancashire for St Albans, Hertfordshire. A huge culture shock. “The locals couldn’t understand me and I couldn’t understand them. This was 1959, before Coronation Street, and nobody had heard a Lancashire accent. I had to learn to speak southern.” At 13, she was hanging out at a teenagers’ club attached to folk pub The Cock. “I really got into folk, and trad jazz – anything you could dance to. Ska too. I used to listen to Prince Buster, I was a Mod, I had a Lambretta, in ’63 or ’64. I was still at school but I saw Georgie Fame at the Flamingo Club. So much was packed into a few years. So much energy.” Maddy, whose father Allan co-created TV’s Z-Cars, started performing in The Cock, where she befriended future folk star Donovan. “You could come up from the floor and have a go, and people weren’t judgemental. I liked that. It gave you a chance to start and gain confidence.”

She became half of folk duo Mac & Maddy with Keith ‘Mac’ MacLeod. By 1966, Maddy was performing with the late multi-instrumentalist Tim Hart; the pair became the backbone of Steeleye Span, formed with former Fairport Convention bassist Ashley Hutchings in 1969. “We were living in Archway, north London, when Ashley and Terry Woods came round to dinner and asked if we wanted to join a folk-rock band. “Folk clubs were brilliant, but they could only really afford to book two people. We were looking to be something more.”

Fellow singer and future member Martin Carthy suggested their name, taken from traditional folk song, Horkstow Grange, which related the story of Lincolnshire foreman John Bowlin and his enemy, waggoner John Span, nicknamed Steeleye. “It was an old term for a hard man. The only other time I heard it used was about Lee Marvin’s character in Cat Ballou.”

With Terry’s wife Gay sharing vocals, the band started rehearsing the next day. But the recording sessions for their debut album were so fraught, the Woods left before the LP was released in June 1970. They were replaced by Carthy and fiddler Peter Knight – Steeleye Span’s line-up changes, too numerous to mention, make the Middle East seem stable. “In the 70s we were either fighting or laughing, sometimes both at the same time,” she says.

Their first live performance was on John Peel’s radio show; their first gig was at the Cambridge Folk Festival that summer, followed by the university circuit. In 1973, they toured America supporting Jethro Tull. Singer Ian Anderson wryly warned Maddy, “The Americans had a hard time getting us, there’s no chance with you.” He was joking but he was right. They never made the Billboard Top 100, but they loved every minute. “We did five nights at the LA Forum – we’d never done anything like that before. It was like having a residency. We got a drummer in, Nigel Pegrum, just for that tour.”

Their pal David Bowie played sax on their 1974 cover of Phil Spector’s To Know Him Is To Love Him but Steeleye Span’s biggest album was 1975’s All Around My Hat, produced by Mike Batt. It went Top Ten and stayed on the chart for six months. Their rockier follow-up Rocket Cottage, also produced by Batt, tanked despite containing fan favourites like London and St James the Rose. Why didn’t London chart? “Some songs come out of the radio, some don’t. Now they build them to do that. The Eurythmics, who we knew, put out Love Is A Stranger in 1982 and it didn’t happen. Their label, RCA, told them ‘We’ll try one more’, and the next single Sweet Dreams went platinum. Then they re-released Love Is A Stranger and it went Top Ten.”

Music industry rascal Tony Secunda managed them in the 70s. “In Australia he set up a competition for fans where whoever won would get to spend 24 hours with any member of the band they liked. The papers were outraged. It was claimed we were going to be deported…” Except it wasn’t remotely seedy. The winner chose to spend her time with then guitarist Bob Johnson but brought her boyfriend along. “They just sat chatting until 2am.”

Gigging used to unnerve Maddy. “When we had a gig, I’d be terrified all day long. But we laughed a lot, drank quite a lot, and playing was the height of excitement. I used to run around the gig at the end just running off adrenalin.” She only fell off stage once. Span had some success in Holland, Sweden and Germany but she admits, “We never worked Europe hard enough.”

Maddy, who has released 14 solo albums, has saucier band stories that she says she might tell one day, “but I’d either have to be very brave or they’d all have to be dead…” She married their bassist Rick Kemp in 1978 and had two children, singer Rose and guitarist Alan, before divorcing. Kemp and Pegrum were involved in a mischievous (and filthy) 70s spoof punk band called The Pork Dukes. Span’s famous fans included the late fantasy author Sir Terry Pratchett who picked Thomas The Rhymer for his Desert Island Discs. They played his 60th birthday party and collaborated on the 2013 album Wintersmith, based on Pratchett’s novel of that name. Quo loved them too. Maddy was in their mosh pit just after Quo released their 1996 cover of All Around My Hat. “Francis saw me and told the audience I was a lookalike. Then he loooked again and said, ‘**** me, it is Maddy’ and I was hauled on stage for the encore. It was all very jolly.”

Now the band’s only original member, Maddy lives in northeast Cumbria. She was awarded an MBE for services to folk in 2001 and teaches in her local arts centre. Her favourite Steeleye Span songs are the Scottish ballad Tam Lin, trad song The Lark In The Morning and the prog-rocking Bonny Black Hare. They tour next month until December 19, supporting their critically acclaimed 25^th album, Conflict, which includes a folk-ska song. Maddy has no unfulfilled ambitions. “I’ve been lucky,” she says. “I’ve been able to do everything I’ve ever wanted to do.”

*Maddy Prior tours the UK with Steeleye Span from 16 November, in support of new studio album Conflict.