There is no accurate count of how many witches there are in the UK as witchcraft is a diverse and often private practice. Additionally, not all individuals who practice witchcraft may identify openly as witches.
Yes, they do practice in the UK. It is called the Olde Religion there.
Witches' Brew - 1980 is rated/received certificates of: UK:15 USA:PG
The Witches Hammer - 2006 is rated/received certificates of: UK:15 USA:R (certificate #45584)
What Witches Do has 223 pages.
Witches of the Caribbean - 2005 V is rated/received certificates of: Argentina:16 UK:15 USA:R
The traditional number of witches in a coven is 13.
A Cauldron of Witches has 127 pages.
The Witches of Chiswick has 336 pages.
Whispering to Witches has 280 pages.
A Community of Witches has 148 pages.
The Witches of Karres has 202 pages.
The Witches of Worm has 192 pages.