Reviewed by: Laura Keynes NYRB/Vintage classics, 240pp, £8.99Tablet bookshop price £8.10       Tel 01420 592974First published in 1976, The Alteration imagines an alternate 1970s England in which there has been no historic break with Rome: Martin Luther had become Pope, and Arthur Tudor and Catherine of Aragon had produced a son. England is still Catholic, frozen in time. Citizens live under a medieval ideology: electricity has been banned, and people eat off pewter plates.The book’s hero is Hubert Anvil, a 10-year-old chorister with a faultless voice. To preserve his voice, the Vatican hierarchy decrees surgical castration.Hubert is told this is God’s will for him; he must obey. But Hubert is curious about sexual desire: what is this stran