"It's sometimes called The Chariot"

This article describes the dangerous nature of this story for religious scholars and describes Ezekiel - chapter 1, where the Chariot appears. This Wikipedia entry also goes in to some detail on Merkabah, otherwise known as The Chariot, describing a very different form from Pullman's; it is formed from four angels each with four heads and so on.

Pullman, however, does put to rest any debate on who is sat upon the Throne on the Chariot. For religious scholars it was impossible for it to be God as God cannot speak to humans, though it spoke with his authority. Pullman answers these with the Lord's Regent, Metatron, who speaks on God's behalf.

The Chariot is also referred to as the 'chariot of fire' in Blake's poem 'Jerusalem', which provides an epigraph later in the novel.