Escorts in W1K and W1J, as the Society arranges them after dark on both sides of the line

W1K covers the ground from Oxford Street down to roughly the line of Mount Street and Grosvenor Street, and west to the park. Grosvenor Square sits in the middle of it, with the receptions and the hotel function floors. Mount Street runs along its southern edge and holds most of the district's tables. The northern stretch of Park Lane belongs here too, which is where the ballrooms are.

The addresses in this postcode include W1K 4HR on Brook Street, W1K 2AL on Carlos Place, W1K 1QA and W1K 7TN on Park Lane, W1K 2HP on Grosvenor Square and W1K 6TF on the small square behind it. We give the address rather than the name. Three companions live inside it.

W1J begins where W1K stops and runs down to Piccadilly and the park railings. Berkeley Square is its centre, and the streets off it, Charles Street, Curzon Street, Half Moon Street, account for a good share of the Society's later evenings. Piccadilly forms its southern boundary and Green Park its south western corner.

The rooms here are smaller and often older: W1J 8LT on Stratton Street, W1J 7BJ facing Green Park, W1J 7BH on Half Moon Street, W1J 5EB on Charles Street and, on the corner where the postcode ends, W1J 9BR itself. Serviced flats and mews houses make up much of the rest.

The boundary wanders. Berkeley Square is W1J, the top of Davies Street is W1K, and Berkeley Street carries you from one to the other in ninety seconds. Bond Street, a few minutes north east, is W1S and has a page of its own.

For the Society the distinction is practical rather than territorial. Both postcodes are served by Green Park, four minutes from the square on the Victoria, Jubilee and Piccadilly lines, and by Bond Street five minutes north, from which the Elizabeth line reaches Heathrow directly. Hyde Park Corner, on the Piccadilly line, lies roughly seven minutes from the western edge of either.

Give Cressida the hotel and the room number, with the name it was reserved under, or, for a flat, the street and the bell to press. She repeats it back in writing, tells you the moment your companion sets out, and needs nothing more. Her car is paid for by the Society throughout the first two zones, which takes in both postcodes and a great deal besides.

A single hour is £600 and ten hours are £3,000, with everything between them printed on the rates page. Angelika, Luna and Samanta live inside these two postcodes and know most doors already, and the roster holds the other twenty-five.