Tea sets have changed regularly over the years since tea first became sufficiently common in England and Europe to warrant its own service pieces. The term "proper English tea set" isn't precise. However, understanding the history and development of tea services can help you choose a set that is proper in regard to both tradition and the use you intend for it.
European Tea Services
Tea became popular in Europe during the 1600s. At this time in France a form of tea service developed that established the core pieces. Services were often made of silver, pewter or other metals, as these would go with almost any porcelain used for tableware. By creating a very clear serving set there was less need to consider the pattern of the cups, saucers, plates for foods to be presented with tea, and the flatware.
The Developing Central Pieces
Over time, the central pieces of a classic tea set came to include a tea pot, usually short and stout to allow tea leaves room to expand and steep; a coffee pot for those not interested in tea; a waste bowl to receive spent leaves before brewing a new pot from fresh water; a sugar bowl or basket and a creamer; and a tea caddy to hold the dry tea leaves before brewing. In some instances a matching silver serving tray was included as part of the set.
China and an Expanding Selection
During the Victorian era, the high standards of English bone china combined with a tendency to elaborate almost all aspects of place setting and food presentation led to extensive sets with specialized serving pieces and tools. Bone china sets were often in a single china pattern, with serving places, cups, saucers and individual plates, plus specialized serving plates for foods all matching. In this situation a tea set could grow almost indefinitely, allowing owners to elaborate their sets with add-ons.
During the 20th century, simplicity regained control, and in the process some classic elements of the tea set altered. Coffee pots, while often part of modern silver sets, are commonly left out of china sets entirely. The waste bowl, which was used to contain spent leaves, seldom appears in any tea modern tea set. Instead, sieves and strainers are used to contain the leaves, and are removed before serving. The sugar bowl and creamer remain part of a service. In the case of a fine china tea set, one usually purchases at least four cups and saucers to go with the core serving set. This leaves two different versions of tea services--those produced in metals, and those produced in fine china. The metal sets tend to include tea pot, coffee pot, sugar bowl or basket, creamer and often a matching tray. China sets generally include a tea pot, sugar bowl, creamer and a set of four matching cups and saucers.
China tea sets are still expandable. The expansion options are usually more limited, as there is little modern demand for highly specialized pieces. Common expansions include add-on sets of cups and saucers, matching plates of salad or lunch size, and matching presentation servers for foods. It is not uncommon to find small food items served on a metal three-tiered stand used to hold plates of a pattern matching or complementing the primary tea set. Similarly, full-sized plates or even platters of a matching or coordinating pattern are within the bounds of a proper English tea set. However, remember that beyond the core pieces of a service, additional pieces are flexible and can be assembled at the discretion of the owner. When in doubt, the primary concern is preference, rather than bondage to a set pattern.