Escorts in Green Park, W1J and SW1A, with the deck chairs stacked and the lamps lit on the Queen's Walk

Green Park keeps the shape it had when it was a hunting ground, and its refusal to plant bedding flowers has hardened over the years into a point of pride. The result is a long triangle of grass and mature trees between Piccadilly and Constitution Hill, dotted with deck chairs from spring to autumn and crossed by paths that all seem to finish at a good address. The Canada Memorial sits over towards Constitution Hill, a low granite slope with water sliding over it and maple leaves cut into the stone.

The Queen's Walk runs the whole eastern edge, from Piccadilly down to the Mall, and it is the most civilised way there is to move between Mayfair and St James's on foot. At the Piccadilly end the park is entered through a set of tall gates rescued from Devonshire House, and the station beneath them wears a frontage of pale Portland stone that reads more like a gallery than a ticket hall.

Almost everyone who asks for Green Park is staying within three minutes of it. The park is the reason the hotels are here and the reason the rooms cost what they do, and a guest who has paid for a window facing the trees generally wants an evening that uses it. That means an early drink rather than a late one, a walk before dinner rather than a taxi after it, and a table booked for eight because the light at seven is too good to waste.

It suits a first meeting for the same reasons. There is somewhere to sit outside, somewhere to walk if the conversation wants moving, and half a dozen bars within a short stroll if it wants extending. £750 buys two hours, enough for a drink, the Queen's Walk and a table, which is why two is the shape Bella pencils in most often for this postcode.

W1J 9BR is the corner itself, with its arcade along Piccadilly, the Palm Court under the glass and a dress code in the restaurant that still means a jacket. Two minutes west, W1J 7BJ is recognisable from across the road by the wall of living plants growing up its front. Behind them, up Stratton Street and then Half Moon Street, stand W1J 8LT and W1J 7BH.

On the SW1A side, tucked into the cul de sac of St James's Place, SW1A 1NJ faces SW1A 1NY across a few metres of very quiet paving, close enough to the park gates that a guest at either can be on the grass in ninety seconds.

Those six are geography. None of them knows us, none of them will be told, and nothing about your evening reaches a front desk. She gives your name downstairs if that is the plan, or goes up unaccompanied after Bella has written down the floor, the number and whose name the booking carries.

The station sits about 1 minute from the park gates. Three lines run beneath it, the Jubilee, the Piccadilly and the Victoria, which buys a change free ride out to the airport and a direct one to the Eurostar platforms. A walk of 6 minutes west along the railings brings Hyde Park Corner; 8 minutes east brings Piccadilly Circus and the theatres.

She comes by car, the first two zones priced in before you heard a figure. On the night, a W1J booking usually has her at your door about an hour after confirmation, longer when Piccadilly locks up in the evening rush, and Bella sends the exact time in the chat once she is under way; one entered in the diary days earlier opens at the hour written there. The fee passes from you to her at the threshold, and the room goes into a message beforehand.

Sonya tells this one with her hands. A guest at SW1A 1NJ, four hours from five, who had asked Bella for somebody calm. She arrived in the St James's Place cul de sac in flat shoes and a camel coat, carrying the heels in a bag, which he says was the moment he relaxed.

They walked the Queen's Walk down to the Mall and back while the light went orange, took the last two deck chairs of the afternoon, and reached the Palm Court in time for the harp. Dinner afterwards was late and small. Four hours, £1,300, and a note to Bella that read, in full, more of that please.

Samanta and Luna both live in Mayfair, just across Piccadilly, and both know the difference between a Piccadilly corner evening and a Half Moon Street one. Lea and Patricia come across from Belgravia through Hyde Park Corner, Lea with a paint chart in her bag and Patricia with a novel she will quote if you let her.

Sonya and Bianka travel in from Knightsbridge, one for the posture and one for the wine list. Lucy comes up the Victoria line from Pimlico, dark curls and a very precise order at the coffee counter. Six or seven names on any given evening, and Bella names the one who is actually free rather than the one who photographs best.

Walk east along Piccadilly and the arcades of Piccadilly begin within a block. Drop south along the Queen's Walk and you are in St James's, all shirtmakers and club steps. North up Berkeley Street lies Berkeley Square and its late doors, and beyond it the whole of Mayfair.