How did a sacramental brew, prepared with hand-rolled leaves and buds from a mountain shrub, infused in boiling spring water and served in delicate porcelain cups to thoughtful sages, become a box of bags hastily shovelled into metal pots beneath steaming spouts, poured into thick mugs and gulped down with milk and bacon sandwiches?

The story of tea, the staffroom mainstay, and its part in the national story of Great Britain is a fascinating one to which Roy Moxham pays wry, idiosyncratic homage. Hinging his historical account on the year he spent helping to run a tea plantation in east Africa, he covers several centuries and continents, fads and fancies and bits of social history.

Camellia sinensis and the drink that could be made from its leaves was a Chinese secret for hundreds, maybe thousands of years. Sometime in the 16th century the Portuguese, inveterate travellers and traders, got hold of it.

In the 17th century, Charles II, who married a Portuguese princess, fostered its introduction into England as part of a general relaxation and expansion of manners after the Puritan interregnum.

Like coffee and hot chocolate, tea became a drink taken with politics and newspapers, to accompany gossip. Not for some time did toast and cake enter the equation (the first afternoon tea-party is recorded in the early 19th century) but sugar, absent in China, was there in England from the beginning: imports of sugar multiplied tenfold during the 18th century, keeping pace with imports of tea. Along with its role as social facilitator, tea was planted as part of the iron hand of empire. Though much of India is too hot and low-lying to grow tea, there were some native shrubs in Assam and Darjeeling. When these were cross-bred with Chinese seeds, the way was clear for a massive forest clearance and planting exercise in the first half of the 19th century, speedily followed by a similar programme in Ceylon (now Sri Lanka).

Conditions for workers in these plantations were cruel - most white managers scorning the idea that their captive labourers, bound by indentures they scarcely understood, had any human needs. Conditions were especially hard in Ceylon, where workers from Tamil Nadu were urged over the Straits of Ceylon and a gruelling mountain range, only to earn minimal wages and live with filth and disease. Most died.

The same story has been repeated in eastern Africa, and wherever tea has been grown. Harvesting the shrubs is back-breaking work. It is best done when the dew is on the bush, and only the first “tippy” shoots should be taken. This process is repeated several times over the growing season and needs skill and attention: mechanised tea-harvesting is wasteful and can damage the plants. But though tea needs its workers, as a commodity it does not command good prices. Individual plantations were, and are, decently run, but “coolies” have been abused as badly as miners or rubber-tappers.

So when you next visit the supermarket or chip in to the kitty for teabags, buy fair trade tea. Not only does it benefit workers directly, it also encourages other producers to join the scheme.

Moxham is not an activist for tea-workers’ rights, though. His is a more indirect approach, switching from 18th-century handbills to glimpses of 19th-century docks and discussions of war rationing of tea. Lyons Corner houses and the rise and fall of Sir Thomas Lipton, entrepreneur credited with inventing the tea bag, Brooke Bond (there never was a Bond, he was invented to make Brooke’s company sound posher) and opium wars all jostle each other in a book that is less a linear history than a superior box of assorted nuggets. Quite the ideal accompaniment to a nice pot of golden tippy orange flower pekoe (accept no substitute).