The plan for the Harley estate published by John Prince in 1719 accurately foreshadows the position and alignment of Castle Street as well as its name. The origin of the name is mysterious, but the likely reason is that the street pointed eastwards towards traces of one of the biggest of the Civil War fortifications round London. This according to George Vertue was ‘a large Fort with Four half bulwarks, across the road at Wardour Street’, which if accurate would mean it impinged on the line of Castle Street at what is now Berners Street, just beyond the confines of Harley property. The ‘castle’ in question was distinct from a minor fort further east which probably gave its name in the 1670s to Joseph Girle’s Castle Inn, on Oxford Street near Hanway Place.1 In due course Castle Street spawned its own Castle pub, at the southern corner of the former Bolsover Street. It was rebuilt in an equivalent corner position in the 1820s when Regent Street superseded Bolsover Street, acquiring its final form in 1866 and disappearing only during the rebuilding of Regent Street in the 1920s.

The Prince plan shows only the western two-thirds of Castle Street as projected in 1719, in other words the portion on Cavendish–Harley property. The thinking then was to break its course with a great market square, a hub for the eastern part of the estate and commercial counterpart to the Oxford Chapel at the smarter west end. Larger even than Cavendish Square, this proposed ‘Marybone Place’ was centred on Great Portland Street along one axis and Margaret Street on the other; Castle Street would have entered and exited near its southern base. That plan was evidently soon set aside as too grandiose, and a smaller market square substituted a little further east and south, flanking the west side of Great Titchfield Street, and aligned east–west. It became an ad hoc, irregular public space, with Oxford Market itself at its eastern end, neither keeping to nor centred upon the frontage line of Castle Street but with its northern edge poking uncertainly forward.

Both ends of Castle Street, west and east of the market, were in simultaneous development by 1722–3. Next to Wells Street, for instance, at the eastern edge of the Cavendish–Harley property, there was early building activity on the garden of the Adam and Eve (sometimes Fall of Man) pub. This pre-existing alehouse lay next to the old footpath now known as Marylebone Passage and enjoyed a garden of more than two acres stretching southwards down to Oxford Street: hence the present Adam and Eve Court, between Oxford Street and Eastcastle Street.

Castle Street stopped abruptly at Wells Street until around 1760, when building began on the neighbouring Berners estate and the line was prolonged eastwards to Newman Street. The two parts of the street had by then acquired their own identities as Little Castle Street and Great Castle Street. By the early nineteenth century the form Castle Street East had generally ousted Little Castle Street (perhaps because there was another Little Castle Street near Leicester Square), to be superseded by the current name, Eastcastle Street, in 1918.

Great Castle Street once enjoyed some coherence. But it was broken into two by the aggrandisement of Bolsover Street into Regent Street, and then saw almost the whole of its south side eaten up by the shops around Oxford Circus. So a street shown on Horwood’s 1799 map with over forty separate houses can now barely muster a dozen independent addresses.

By the early nineteenth century both sides of the street were predominantly in trade use. But whereas the north-side houses had few shop windows and their small back gardens or yards mostly remained open, many houses opposite were explicitly shops with windows to match, while their yards had been built over or backed straight on to large stable yards and coachhouses connected with Oxford Street behind.

Many of Great Castle Street’s surviving buildings are due to James Alfred Michell (1844–1913), a London-born carpenter from a Cornish family which already in the early 1860s was based at 34 Great Castle Street, on the south side close to Regent Street. This remained Michell’s business address for most of his career, combining coffee or dining rooms with a builder’s or developer’s office, which last he eventually transferred to 9 Market Place. Small developments all over the Portland–Howard de Walden estate brought Michell prosperity; by 1911 he was a JP, with a townhouse at 5 Devonshire Place and a country home (Shouldham Hall) outside King’s Lynn. Michell used a number of architects, but by the Edwardian period he was firmly in league with F. M. Elgood, who designed him a number of quite festive fronts in a Renaissance style. All these premises were explicitly planned for the lace and drapery trades, which had achieved absolute dominance along both sides of the street by the 1920s.