score:2
There is no definitive list of "mainstream" denominations in the UK - indeed the term is largely subjective - but there are a number of official and semi-official ways in which denominations are recognised.
The NHS Data Dictionary, based on the international Systematized Nomenclature of Medicine Clinical Terms (SNOMED CT), lists some 80 possible values for Christian religious affiliation - but since this is an international list it is not specific to Britain.
Some denominations self-identify as being mainstream; the URC website says:
Although one of the smaller mainstream denominations, the United Reformed Church plays a dynamic and challenging part in the British Christian community.
Wikipedia provides a comprehensive list of denominations in the UK, categorised into 12 groups (including "interchurch" - ie pan-denominational groups, and Catholicism) but does not indicate which are "mainstream". The twelve groups are:
Interchurch
Anglican
Baptist
Catholic
Holiness & Pietist
Lutheran
Methodist & Wesleyan
New Church Movement
Orthodox
Penticostal
Presbyterian & Reformed
Other
The Methodist Church website contains a basic introduction to Christian denominations which contains some links to some other useful resources. The World Council of Churches lists 11 member churches that are based in the UK while Churches Together in Britain and Ireland lists several more member churches. Since none of these lists are an exact match for one another it is fairly clear that no definitive list exists, but that lots of denominations are "recognised" by some larger organisations.
What constitutes "official" could also be somewhat subjective. It is well known that the Church of England is the officially established church in England. The Church of Scotland, Church in Wales and Church of Ireland are not, however, officially established. (The Church of Scotland is an unusual case where some official documentation implies the church is officially established, but the church themselves disclaim this.) (Source: good old Wikipedia)
Nevertheless there have been a number of Acts of Parliament relating to individual denominations; this does not of course make them official state churches, but does at least show that they are recognised by the state. Examples include:
Upvote:0
'Mainstream' is not a word with a clear definition, so there is never going to be a definitive list of such things. You can always make arguments for including/excluding different groups. You have made an obvious omission: you've only listed English denominations, although you talked about British ones. If you want to include all UK mainstream denominations you should certiaily include the Scottish ones, especially the Church of Scotland (and assuming you count the Episcopal Church of Scotland as Anglican for your purposes), and also Northern Irish ones.
Apart from that the list you've made is a pretty good one, and I can't think of others with obvious cases to include them. The others listed in the US list have very small presences in the UK. You might also consider that Baptists come in different flavours.
In answer to your second question, the only form of official recognition is the special privileges granted to the Church of England as the state church. These days these are largely ceremonial.
Upvote:4
This 2007 report entitled Churchgoing in the UK has a vast array of demographic data on churchgoers in the UK. It even differentiates between regular churchgoers and those who just state affiliation.
For example, among regular churchgoers surveyed, the denominational breakdown is:
All these are defined in the report (especially Appendix 1 Figure 10). This should answer mainstream as in "most common." Mainline is defined as a specific doctrinal stance in the Wikipedia article you link, so denominations on that list would be "mainline Protestant" there too. Though some don't exist there, I think there aren't any that exist there that aren't here/in that master list.