The A5204 is a short route in the West End of London. It is the first A52xx road to be created following the original 1922 classification, presumably dating the road to the mid-1920s. The road was originally the B506 but took over that road between the A5 Edgware Road and the A4201 early on, before taking on more of that road to its current eastern terminus of the A400 Tottenham Court Road.
The road starts at traffic lights on the A5 Edgware Road, just to the north of that road's starting point at Marble Arch. It heads east along Seymour Street to reach Portman Square and traffic lights on the northbound A41. The A5204 now runs along the southern edge of the square to meet the southbound A41 at the next set of lights.
We now continue along Wigmore Street and soon cross Wimpole Street, where the road becomes one-way. Presumably westbound traffic now follows the road one block further south although this is unclassified. One block east we reach Cavendish Square - according to maps all four sides of this is numbered A5204 although there is no reason why this should be so. We continue to cross the A4201 Regent Street and the one-way system finally ends two blocks east of there on Great Tichfield Street.
Now two-way once again the road bends to the left one block further on and we pass into the bohemian district of Fitzrovia and pass along Goodge Street. For the final couple of blocks the road is one-way again and we continue on to end on the A400 Tottenham Court Road, which is itself one-way northbound at this point.