One word answer: "Yes"
Longer answer: The law only provides that you must have a certain number of days paid holiday per year. The current multiplier is 4.8 times the number of days you work each week. (So, for somebody working a 5 day week, that means 24 days paid holiday per year). However, those figure only apply from 01/10/07. Prior to that time (and so for much of 2007) the multiplier was 4.0 (so someone working a 5 day week was only entitled to 20 days paid holiday per year).
As long as the employer provides a reasonable amount of notice, he/she is free to determine the dates upon which you can take your holidays. For example, there is no requirement for an employer to allow you to have any complete weeks off work. It is perfectly lawful for the employer to choose, say, 24 separate midweek days throughout the year so that you never get more than one or two days off at a time. (Nobody has any right to one or more weeks holiday as a block, unless their contract specifically states so).
Chris