Why do so many pop performers produce their best work when they are in their early-to-mid twenties? A simple answer is that pop is essentially a juvenile form, the expression of a certain youthful worldview and rebellious sensibility, and the more the musician matures and learns about music, the greater can be the desire to complicate and to experiment with what once felt so natural and spontaneous.

Few artists experiment more than Kate Bush - often to thrilling effect. Her first single, ‘Wuthering Heights’, was a huge number one hit in 1978, when she was just 19. After that surprise, EMI allowed her near-absolute artistic control. Since 1980 she has produced and written all her own material and, as the wait for each new album has grown longer and longer, she has become the musical equivalent of a celebrated novelist who refuses to be edited: she has the freedom to do whatever she wants and at whichever speed she desires. If she wants Rolf Harris to play didgeridoo for her as he did on The Dreaming (1982) and again on this new album, Aerial, she can have him. If she wants to combine the orchestral string arrangements of Michael Kamen with uninhibited rock guitar, as she does here, she can. If she refuses to play live, as she has done for more than 20 years, no one will try to force her to change her mind.

Twelve years is a long time to wait for a new record from any artist, even from one as consistently inventive as Kate Bush, but at least Aerial offers value. It’s a 14-track double album, no less. The more experimental of the two records is ‘A Sky of Honey’. It begins not with music but with the sound of birdsong, the wind in the trees and the voice of a child calling for her parents. What follows is a suite of seven unashamedly romantic and interconnected songs taking us on a long day’s journey into night and then on through to the next morning when birdsong is heard once more and the whole cycle starts all over again. There are similarities here with the second side of the remarkable Hounds of Love (1985) and to the song sequence ‘The Ninth Wave’ that took us into the consciousness of a drowning woman (the sea, in her work, has long been a source of inspiration and of threat). That album, memorable for its daring, its imaginative use of sampling, and its erotic intensity, was, like much of Bush’s work, preoccupied with memory - and with how we are never entirely free from the voices and sounds of childhood. It remains her best album.

‘A Sky of Honey’ is music of pagan rapture - songs about acts of creation, natural or otherwise; about the wind, rain, sunlight and the sea. Sometimes it is just Kate alone at her piano, her voice restrained. Sometimes, as on the outstanding ‘Sunset’, she begins alone and softly, but soon the tempo quickens and the song becomes an experiment in forms: jazz, progressive rock, flamenco.

There are weaknesses. At times, Bush can be too fey and whimsical, especially on ‘Bertie’, which is about the joy of motherhood, or on ‘Mrs Bartolozzi’, a rhapsody to nothing less than a washing machine: ‘My blouse wrapping itself around your trousers… slooshy sloshy/ slooshy sloshy.’ And the bold, musically adventurous second album is a little too insistent in its ‘hey, man’ hippyish sensibility, with Kate running freely through the fields or climbing high in the mountains. She did, after all, once dress up as a kind of white witch for the cover of Never For Ever (1980), on which she is portrayed flying through the air, like a giant bat.

‘What kind of language is this?’ Kate Bush sings, self-interrogatively, on the title track, the last of the album. It’s a good question, to which she offers a partial answer on ‘Somewhere in Between’, which in ambition and content is where most of the songs on this album are suspended - somewhere in between the tighter, more conventional structures of pop and the looser, less accessible arrangements of contemporary classical and the avant-garde; somewhere, in mood and atmosphere, between the lucidity of wakefulness and the ambiguity of dream; between the presumed innocence of childhood and the desire for escape offered by the adult imagination; between abstraction and the real. Even when she escapes her wonderland to write songs about actual figures in the known world, she remains attracted to those figures such as Elvis (‘King of the Mountain’, the album’s first single) or Joan of Arc (‘Joanna’) that, in death as indeed in life, have a mythic unreality.

So, again, what kind of language is this? It is ultimately that of an artist superbly articulate in the language of experimental pop music. But it is also the language of an artist who doesn’t seem to want to grow up. Or, more accurately, who has never lost her child-like capacity for wonder and for pagan celebration and who, because she is sincere and can communicate her odd and unpredictable vision in both words and through sumptuous music, occupies a cherished and indulged position in the culture. There is no one quite like her, which is why, in the end, we must forgive her excesses and eccentricities. We are lucky to have her back.