Like all new arrivals at the south London jail, the former minister will have been taken into the reception area to be seen by a doctor. He would then swap his possessions for a prison number and a uniform consisting of a blue and white striped shirt, jeans and jean-jacket, and unflattering pumps.
Aitken would have been allowed to shower, and offered a telephone call to his family along with counselling and a meal on a tray.
Inmates at the modern, red-brick prison include some of the most dangerous prisoners in the country, with Category A security classifications. But others are low-risk like Aitken, waiting to be dispersed to another prison or being held on remand pending an appearance in court.
Nevertheless, the ex-minister will be given the option to be held under Rule 43, as a prisoner likely to come under pressure from other inmates because of his position and public profile.
If he wants to be segregated he will spend his time at Belmarsh in the company of sex offenders and other vulnerable inmates. If space is short, he may have to "double up", sharing his cell.
If he remains at Belmarsh for longer than a week he will be given a job. This could involve sweeping the floor as part of the "Yard party", although Aitken is perhaps as likely to be given the red arm-band of the prison librarian.