Westminster, SW1A and SW1P, when the House rises late

The single most useful thing to know is that you do not have to commit to a start time you cannot keep. Write in the afternoon with the length you have in mind and a rough hour, and the desk holds the shape rather than the minute. When you know, send one line and it is fixed. Fifteen minutes of grace sit inside every booking in any case.

Two hours at £500 is the common length for a night that begins at eleven. Three hours at £700 suits the evening that starts at nine and is not in a hurry. The ten hour night at £1,800 is booked by guests who would rather not be looking at a clock at all, and in this postcode that is a larger share than anywhere else on the site.

SW1A holds Parliament Square, Whitehall, Horse Guards and the whole of the river frontage from the bridge down to the Embankment. The Elizabeth Tower stands at the north end of the palace and the bell inside it weighs thirteen and a half tons, which is the sort of detail that survives being mentioned twice.

SW1P is quieter and more residential, running down Victoria Street past the Abbey towards Smith Square and Horseferry Road, where the streets go completely still after eight. Between them the district has more offices than restaurants, which is exactly why the hotel bars matter here.

Westminster station is a minute from Parliament Square on the Circle, District and Jubilee lines, and the Jubilee platforms sit inside a concrete box thirty nine metres deep that is worth looking up in while you wait. St James's Park is four minutes west on the Circle and District, useful for the SW1H hotels. Embankment is eight minutes north east on the Bakerloo, Circle, District and Northern.

The roads here move well after nine, better than anywhere in W1, which means a companion crossing from the west arrives faster at half past ten than she would at seven. Thirty minutes from confirmation is the usual figure, and less from St James's or Pimlico.

SW1A 2BD sits between the river and Whitehall with a courtyard entrance that sees almost no traffic after ten, and a lobby with a chandelier of a thousand glass pieces. SW1A 2EJ was built as a block of flats in 1884 and keeps a terrace looking across the Embankment gardens to the water.

SW1H 0BH is two minutes from the station with a bar that stays open for the late crowd. SW1H 0QW sits up its own courtyard off Caxton Street and keeps a beehive on the roof and a lobby staircase worth arriving down. SE1 7UT is over the river with the best view back at the palace. All are addresses the desk is asked for, with no arrangement behind any of them.

Visitors here for a conference at one of the halls, who finish at six and find the district has nothing to offer between then and bed. People here for two or three nights of meetings in Whitehall. People staying near the Abbey for an event who have a morning obligation and no interest in a late start. And, on sitting nights, a steady number of people who simply do not know when their evening will begin.

What is asked for here, more than anywhere else, is somebody who can hold a conversation with no work in it. It is the one district where guests say so explicitly.

Laura is straightforward company for a part of town that rarely is, and comes in from Paddington in twenty minutes. Margo is the most composed person at any table, including yours, and is fifteen minutes in from Knightsbridge.

From nearby, Lea walks over from St James's in ten minutes, Stacy is composed at twenty two in a way most people take a decade to manage, Violetta comes in from Belgravia and is extremely dry by the second hour, Cindy prefers an early table when the evening allows one, and Vanessa is the choice for a late view and an unhurried night. Everyone on On The Books reaches SW1 on the same figures.

Romilly answers at every hour, in ten to fifteen minutes, on WhatsApp or on Telegram. Give the hour or the rough hour, the length, the building and a name. The reply carries the arrival time and the figure. Her fee goes to her in person, in the first minute of the booking.

One check follows: the full name the booking is held in, the hotel and the room number, matched once in the same thread and used for nothing afterwards. If the House runs on and the evening shifts, one line moves it.

North across the park the clubland of St James's begins in about eight minutes on foot, and the long avenue of Piccadilly a few minutes beyond it. North east along Whitehall, Trafalgar Square opens into the theatres and the Piazza of Covent Garden in fifteen. Victoria and Pimlico lie south west down the same road, and Waterloo is across the bridge. The whole zone is mapped on the Central London page.