In a similar vein to the recent Royal Wedding weekend, this means that employees will be able to benefit from a 10 day break for just 3 days of holiday entitlement.
Whether employees are entitled to the additional day off will depend on the wording of their contract. Those with a contract which states that holiday entitlement is "20 days plus Bank Holidays" will be entitled to the extra day. However, those whose contract states their entitlement is "28 days including Bank Holidays" will not.
It seems sensible to make the most of the extra day's holiday as we do not expect there will be another bonus Bank Holiday for some time; the only other British monarch to celebrate a Diamond Jubilee was Queen Victoria in 1897.