'Black Friday' (as the busiest shopping day of the year) is a purely American concept.
Brits tend to do their High Street shopping at the weekends, rather than on Fridays, so the last Saturday before Christmas has traditionally been the busiest shopping day of the year in the UK. In recent years, of course, (with the growth of Sunday shopping) the whole of the final pre-Christmas weekend has been seen as the peak shopping period although when Christmas Day falls early in the week (as this year) the previous weekend might actually be busier.
While the UK has never has 'Black Friday', the advent of online shoppig means that we've now got 'Cyber Monday':
http://www.itv.com/news/2012-12-03/online-shoppers-cyber-monday-christmas-spree/
Chris