Question: Which band along with two other British bands is referred to as the "unholy trinity of British hard rock and heavy metal in the early to mid-seventies" whose performance was featured in a 2011 studio compilation album at the BBC's Maida Vale Studios?
Context: Oliver Sabin, formerly known as Unicorn Kid, is a Scottish electronic music/chip music composer and musician from Edinburgh, educated at Leith Academy.  When asked about the name of the act, Sabin states "There’s no real story behind the name, it just kind of came about and fitted in with the fun, magical nature of the music."  Sabin has had a number of BBC Radio 1 appearances including an early live session on the Vic Galloway BBC Radio 1 show and a BBC Maida Vale Studios session for Rob da Bank.  In September 2014, he called it quits for Unicorn Kid to pursue a different alias that is yet to be announced. The discography of British singer-songwriter Gabrielle Aplin, consists of two studio albums, four extended plays, three live albums and five singles.  Her first release was the 5-track "Acoustic EP" which was released on the iTunes Store on 13 September 2010.  Her second EP "Never Fade" was released on 9 May 2011 and saw Aplin expand her sound, showcasing a more folk rock sound and playing all instruments herself.  In April 2011, Aplin was invited to perform for "BBC Introducing" at Maida Vale Studios, where she played 3 tracks from "Never Fade" and a cover of the Coldplay song "Fix You".  Aplin released her third EP, "Home", on 9 January 2012.  On 29 February 2012, Aplin announced that she had signed to Parlophone.  Aplin was confirmed as the soundtrack to the John Lewis 2012 Christmas television advertisement, covering Frankie Goes to Hollywood's "The Power of Love", the song reached number one on the UK Singles Chart.  On 12 December 2012, Aplin announced that the title of her debut album would be "English Rain".  In addition, she also unveiled its artwork and release date of 29 April 2013.  However, the album's release date was later confirmed as 13 May 2013.  Aplin announced live on 17 February Radio 1 Chart Show that her third single would be "Panic Cord".  The song originally featured on her Never Fade EP and it was released on 5 May 2013, charting at number 19 on the UK Singles Chart.  "English Rain" charted at number 2 on both the UK Albums Chart and Scottish Albums Chart, while reaching number on the Irish Albums Chart.  In 2014, Aplin released her "English Rain EP" in the United States.  The EP was released on the 6th of May and features 5 songs from her debut album, as well as a cover of Canadian singer Joni Mitchell's "A Case of You".  In 2015, Aplin released her second studio album entitled "Light Up the Dark".  "Light Up the Dark" debuted at number 14 on the UK Albums Chart. Over the years, the British hard rock band Uriah Heep has released 24 studio albums, 13 live albums, 16 compilation albums, 27 UK singles (33 worldwide) and 17 videos.  The band's best selling album is "Sweet Freedom" which was released in 1972 and its worldwide sales are more than 4 million copies.  Uriah Heep's progressive/art rock/heavy metal fusion's distinctive features have always featured massive keyboards sound, strong vocal harmonies and (in the early years) David Byron's operatic vocals.  Twelve of the band's albums have made it to the UK Albums Chart ("Return to Fantasy" reached No. 7 in 1975) while of the fifteen "Billboard" 200 Uriah Heep albums "Demons and Wizards" was the most successful (#23, 1972).  In the late 1970s the band had massive success in Germany, where the "Lady in Black" single was a big hit.  With Black Sabbath, Deep Purple and Led Zeppelin, Uriah Heep became one of the top heavy metal and hard rock bands of the 1970s.  It was there that the solid, but rather mainstream-sounding "Sweet Freedom" (No. 18 UK, No. 33 USA) was created with "Stealin'" released as a single.  Having gained worldwide recognition, the band quit using fantasy lyrics and made an obvious stab at versatility by adding funk ("Dreamer") and acoustic folk ("Circus") elements to the palette. The BBC Symphony Orchestra (BBC SO) is a British orchestra based in London.  Founded in 1930, it was the first permanent salaried orchestra in London, and is the only one of the city's five major symphony orchestras not to be self-governing.  The BBC SO is the principal orchestra of the British Broadcasting Corporation (BBC).  The BBC SO is a resident orchestra at the Barbican Centre, and gives studio concerts from its base at BBC Maida Vale studios.  The BBC SO is also the principal orchestra at The Proms, performing the most concerts of any single orchestra in a given Proms season. "Don't Try" is a song from British indie pop band Everything Everything.  The track was released in the United Kingdom on 16 June 2013 as the fourth single from the band's second studio album, "Arc" (2013).  The single's B-side is a live recording from the Maida Vale Studios of The Korgis' "Everybody's Got to Learn Sometime".  The recording comes from 17 October 2012, where the band covered the track for BBC Radio 1 DJ Zane Lowe. Deep Purple are an English rock band formed in Hertford in 1968.  The band is considered to be among the pioneers of heavy metal and modern hard rock, although their musical approach changed over the years.  Originally formed as a progressive rock band, the band shifted to a heavier sound in 1970.  Deep Purple, together with Led Zeppelin and Black Sabbath, have been referred to as the "unholy trinity of British hard rock and heavy metal in the early to mid-seventies".  They were listed in the 1975 "Guinness Book of World Records" as "the globe's loudest band" for a 1972 concert at London's Rainbow Theatre, and have sold over 100 million albums worldwide. The Live Lounge is a segment on the British radio stations BBC Radio 1 and BBC Radio 1Xtra.  Originally hosted by Jo Whiley on her mid-morning radio show and then by Fearne Cotton from 2009 until 2015.  It is now hosted by Clara Amfo, she has been the host since May 2015.  it exhibits well-known artists usually performing one song of their own and one by another artist, in an acoustic format.  The 'Live Lounge' itself is also a physical room in the Radio 1 studios, from where some of the performances are broadcast; however, due to its size, many are done from the BBC Maida Vale Studios.  From 2009, Trevor Nelson began hosting Live Lounges on his BBC Radio 1Xtra show, and was replaced in that slot by DJ Ace in 2017. Maida Vale: The BBC Radio One Sessions is a compilation album by Van der Graaf Generator, containing eight songs from four different recording sessions at Maida Vale Studios for BBC Radio 1 in 1971, 1975 and 1976, three of which were Peel Sessions.  It was released in June 1994 on Band of Joy Records. Let's Buy Happiness were a British alternative rock music group.  The group consisted of Sarah Hall (vocals), James Hall (guitar/keys), Graeme Martin (guitars), Mark Brown (bass) and James King (drums).  They began playing local shows in hometown Newcastle, England.  Their first EP "No Hot Ashes" was self-released and received national success.  Following this came singles "Six Wolves", "Fast Fast" and "Dirty Lakes".  The band have twice been invited to the Maida Vale Studios for both BBC Radio 6 Music and BBC Radio 1.  Dirty Lakes has also been included on Spotify's "Songs of 2011" list.  Their tour manager was Alex King who is the brother of former drummer, James King - their father is Hairy Biker Simon King. BBC Sessions 1968–1970 is a 2011 studio compilation album featuring performances by the British hard rock band Deep Purple that were recorded at the BBC's Maida Vale Studios, London, and originally broadcast on various BBC Radio shows from 1968 through 1970.  "BBC Sessions 1968–1970" is a two-disc set collecting all the surviving sessions in the BBC archives.
Answer: Deep Purple