Only the mosaic in the doorway of Number 11 Broad Street, Oxford, reminds passers-by these days of the lovely, rambling old bookshop that operated there from 1870 to 2003 — when the business, specialising in antiquarian and foreign language books, and by then largely Internet-based, moved to Faringdon, where it still flourishes.

The mosaic spells the word Thornton and commemorates Joseph Thornton who originally founded the booksellers in 1835 in a small shop in Magdalen Street with just £250 capital. The business passed from father to son until 1983 when it merged with Holdan Books and was saved from bankruptcy by the Meeus family.

But the name Thornton lives on in Oxford — and indeed worldwide — in the shape of the international firm of accountants and business advisers Grant Thornton, who last month moved their Oxford branch with 111 staff from Botley to the Oxford Business Park.

Extraordinary how firms evolve and change until only the name remains to remind succeeding generations of long lost connections, like Christmas baubles made by children long since grown up or even dead, but still reverently stuck on the tree each year. In the case of Grant Thornton, the connection to the bookshop is that Reginald Walker Thornton, a son of the then Broad Street bookseller John Henry, set up as an accountant together with a partner in 1904 in a first-floor room, divided in two by a curtain, in Lloyds Bank Chambers in Carfax, Oxford. The first year’s balance sheet showed a profit of £105.15s.

In such unremarkable circumstances was born the company of Thornton and Thornton. But the firm hit the big time a few years later when John Thornton got chatting with someone in the waiting room of the Inspector of Taxes. He learned that the stranger had a point to argue over his tax assessment and, always on the lookout for business, told him he was silly to deal with the it himself.

“Well, you had better deal with it for me,” said the stranger — who turned out to be none other than the future motor magnate William Morris, destined in due course to become Viscount Nuffield and Oxford’s greatest benefactor.

Thereafter, as the Morris Motor Company grew and prospered, so did Thornton and Thornton. From such small acorns do great oak trees grow.

At that time, Mr Morris must have been embroiled in what he always afterwards referred to as “that bus business” along with the extraordinarily charismatic solicitor, future Liberal MP for Oxford, and founder of the Oxford Mail, Frank Gray.

“That bus business,” which very nearly led to the arrest of Mr Morris, began in 1912 when he wrote to Mr Gray asking for help in establishing a motor bus company in the city to replace the horse-drawn trams that then still plied the streets. Such an idea was controversial because the city council (or Corporation as it then was) had got itself into a legal tangle with contracts with two electric vehicle companies — one of which, incidentally, wanted to introduce a hybrid electric-petrol tram system.

To cut through the deadlock, Morris and Gray introduced a service unilaterally and illegally. Inevitably, among those who climbed aboard the first bus was a police inspector who told Mr Gray: “I take note that you and Mr Morris take full responsibility for this breach of the law and anything which may result.”

Later, despite opposition, Morris and Gray borrowed £8,000 from Gilletts (later part of Barclays), which had branches in Cornmarket and Banbury, and set up a full service with 16 buses. Such extraordinary going-on must have taxed even the shrewdest accountant — so little wonder the company of Thornton and Thornton in time went on to join forces with an American firm and become the giant it is today.

But talking of names, here is a footnote reference to a Thornton who definitely had nothing whatsoever to do with any accountant. In May 1938, Lord Nuffield agreed to meet a journalist calling himself John Bruce Thornton at his home, Huntercombe Place, Nuffield. In fact this ‘Thornton’ was a kidnapper called Patrick Boyle Tuellman who had drafted a letter to hand to Nuffield when they met. The letter began: “I am packing two automatic pistols of a large calibre and will immediately shoot you through the guts if you attempt to raise alarm or suspicion.” Luckily the police infiltrated the plot with an informer, and Mr ‘Thornton’ got seven years.