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.
The Witches of Eastwick has 320 pages.
A Hornbook for Witches has 70 pages.
The Witches of Karres has 202 pages.
The Witches of Worm has 192 pages.
A Community of Witches has 148 pages.
Witches Three has 423 pages.