Just as magic has always been a part of the world, so have magic users. The earliest records of what we now call witches are ancient burial sites: bodies found buried with the tools needed to continue practicing wherever they went next, in the way that warriors were buried with their weapons and rulers their symbols of office.
Practitioners of magic are found all over the world. In the UK, they are primarily known as witches (a gender neutral term), though other terms are sometimes used - magician or occultist are fairly common, as are discipline-specific terms such as mathemancer.
Unlike in some countries, in the United Kingdom, witchcraft has always been a rather disorganised affair. The institution of the ‘village witch’ has been around since the Saxon era in some form or another. These individuals - for they were, typically, individuals - tended to live somewhat to the edge of society, a part of the community but not really, passing down their knowledge to selected other individuals (often but not always their children). It is common for children brought up in households where magic is practiced to have a greater affinity for magic later in life, much as children brought up in musical households are likely to have an affinity for music.
While generally a fairly ordinary and accepted part of society, at times witches were viewed with suspicion. After all, they were capable of wielding powers well beyond what ordinary people could consider. The belief that angels and demons were associated with the Biblical creatures of the same names only added to this mistrust. James I was particularly concerned by the power of witches, seeing them as a threat to his authority within the country. This led to a climate of fear which only grew during the Civil War, as people looked for a scapegoat to blame for the problems they faced. The majority of witches during this time hid themselves - a feat made easier by the powers they possessed - and, tragically, given the lack of universal distinguishing features, many innocent people were executed for the crime of witchcraft.
However, the 17th century was also a pivotal period in the development of the scientific method and the birth of enlightenment thinking. Despite the threat of arrest and execution, several scholars pursued an interest in witchcraft. The most notable among them was Tamesine Raleigh, a scholar at Merton College, Oxford.
Although her work was in many ways limited, it laid the groundwork for the acceptance of magic as a branch of science, as well as the foundation of what would later become the Slough Institute. Her book, Principia Magicae, details the ways in which magic can be seen as a mere extension of existing knowledge, and a skillset available to any who should choose to study it. The book was much discussed by the educated of the day; while few had a practical interest in magic, the political and philosophical implications were sufficient to warrant significant attention. The Principia was followed by a steady trickle of further scholarly work concerning the nature and practice of magic, legitimising it in the eyes of both academia and the law.
The Witchcraft Act 1735 officially made it impossible for witches to be persecuted purely for pursuing their craft - though, of course, any crimes committed using magic could still be tried in the usual way.
Some people were concerned about the increasing openness of magical knowledge. What had been a folk art passed down from one generation to the next was now a legitimate scholarly pursuit. There were concerns both that magic would become a sort of gentleman's hobby, rather than a craft of the common people.
In a way, the fears were justified. The research being done in Europe's universities was written in Latin and debated in small, select circles of academia. While summoning demons and casting charms never became a mainstream 'hobby', the new techniques and developments were hardly accessible to the working classes, or the village witches of before. However, in another way they did not come to pass - while there were certainly developments being made which were not used by the majority of people, these broadly didn't affect the majority of witches, who continued to be organised in loose communities and to pass on their skills by practical lessons or, as literacy spread, by handwritten books containing their knowledge.
The two sides of witchcraft developed in fairly distinct ways for a couple of hundred years, scholarship rigidly charting different facets of magic - writing treatises on how magic works and how everything is interconnected. Meanwhile, people continued practicing magic on a personal or community level, sharing knowledge of specific rituals and information. In both ways, magic remained somewhat closed off - to access the scholarly branch, the aspiring witch had to be in the position to dedicate time to study in universities, or to know people who did. To access the folk side of things, the aspiring witch simply had to know the right people.
The two styles of magic were brought together again in the 1920s, when the Slough School published the first edition of Elementary Magic, now the standard text for learning the basic magical arts. This simple guide made the academic discipline of magic easily accessible to anyone with the capacity to purchase and read a book. Slowly, the academic knowledge began to spread.
However, by the 1980s there was a widespread fear that the spread was too pervasive. People were, by and large, using the official, scholarly ways of doing magic rather than the traditional, and there was a concern that the magical traditions which had been handed down were dying out - and taking with them valuable knowledge that wasn't covered by academic magic in the same way. There was an attempt to record the spells and rituals that had been passed down through less conventional means. Several studies were carried out, involving large numbers of witches across the country, and indeed internationally.
The birth of the internet saw large amounts of traditional knowledge migrating online, and a further increase in the accessibility of magic. Collaboration in exploring magic, both for scholars and those taking a more casual attitude to magic, became much easier, and information became far easier to access: while before, finding the ritual needed to summon a demon who take days of poring through library books, now they could be accessed through a quick google of the attributes needed.
Witchcraft is currently enjoying something of a boom. It can be difficult to draw a line between witches and non-witches. They have no real shared characteristics, save, perhaps, an interest in magic and a desire to practice it. Some have attempted to define witches as those who have had contact with celestials, which of course leads to the problem of defining 'contact', not to mention the thousands of people who practice purely ritual-based magic. Other have attempted a minimum threshold of practicing a certain amount of magic in a year to be classified as a witch. Still others have attempted (unsuccessfully) to implement some sort of standardised test one would have to pass to be considered a witch.
As things stand, whether or not one is a witch is largely a question of self-definition. If you consider yourself to be a witch, you are one. Under this definition, most estimates as to the number of witches in the United Kingdom put them at around 20-30,000.
The majority of witches take a fairly casual approach to their practice. Most will cast protective charms or good luck spells, using small amounts of personal magic and casting well-known spells and charms. Others take different approaches. Some have dedicated their lives to magic, whether by becoming a magical scholar or by selling their magical abilities to those who would like the benefits that magic can give without having to deal with all the tedious study it requires, or by taking on a full-time role in one of the assorted magical groups which exist.
Many more walk a middle path, with witchcraft and magic being a fairly serious hobby. They tend to be part of groups - whether larger, international groups such as the White Quill, or smaller, local or university groups.
There is no ‘national curriculum’ for magic. Some universities run courses looking at magic, normally from an entirely academic and historical perspective. For those looking for a more practical approach, the Slough School offers regular night classes, both at their base in Slough and in most major UK cities. In addition, a great many informal clubs, groups and societies exist to allow people to learn magic in a more relaxed setting - an extension of the historical practice of small groups passing down knowledge, although admittedly with a far greater access to resources. For those unable to make even these, there is a wealth of written and online resources, from the ubiquitous Elementary Magic to Youtube tutorials in summoning demons. Witchcraft, on the whole, is a rather haphazard affair.