Since 1 October 2007, all workers have had a statutory right to at least 4.8 weeks paid annual leave (24 days paid leave if working a 5 day week). From 1 April 2009 this entitlement increases to 5.6 weeks (28 days). This is a minimum entitlement - employers can choose to offer more.
Holiday entitlement for part time workers is calculated on a pro-rata basis.
The holiday entitlement can include bank holidays. If your workers already receive paid time off for bank holidays in addition to their 4 weekly holiday entitlement, then their holiday entitlement has not increased.
From 1 April 2009, payment in lieu will not be permitted, although payment in lieu of any leave above the statutory entitlement can be allowed (depending on the employment contract).