The main day for Sikhs to go to the gurdwara for worship in Britain is Sunday. This is not for any religious reason, but because Sunday is the day most people in Britain do not work.
The dates of Sikh festivals have traditionally been defined using a lunar calendar, with the result that the festivals were not on the same Western date each year.
Recently a new calendar has been introduced to fix this problem by lining up with the Western calendar so that Sikh festival dates are the same each year.
Unfortunately not all Sikh organisations approve of this calendar, with the result that there are now several dates for most festivals, depending on the calendar you choose.