It is forbidden to eat, drink or smoke in public during daylight hours during the month of Ramadan. The law is strictly enforced.
The public practice of any form of religion other than Islam is illegal; as is an intention to convert others. However, the Saudi authorities accept the private practice of religions other than Islam, and you can bring a Bible into the country as long as it is for your personal use. Importing larger quantities than this can carry severe penalties.
Islamic codes of behaviour and dress are strictly enforced.
You should carry a photocopy of your passport for identification. Make sure you have included emergency contact details.
The Saudi legal system differs in many ways from the UK. Suspects can be held without charge and are not always allowed quick access to legal representation. The Saudi authorities have detained witnesses and victims of crimes. If you need consular assistance, British Embassy staff will try to visit you as soon as they are aware of the case, but in some instances Embassy staff have not been permitted to do so immediately or have had access limited.
Anyone involved in a commercial dispute with a Saudi company or individual may be prevented from leaving the country pending resolution of the dispute. Government bodies often retain passports for official purposes; sponsors also sometimes retain passports, although this is illegal.