I presume you work the equivalent of 4 days a week? 1/2 day Monday and Friday and three full days.
An employer?s obligation to part-time workers must be considered in light of the Part-time Workers (Prevention of Less Favourable Treatment) Regulations 2000 (SI 2000/1551), under which part-time workers are entitled to the same terms as comparable full-time workers, but on a pro rata basis
So you get pro rata what the other employees get - 4/5ths of their entitlement
The employer must ensure that a part-time employee receives his or her pro rated entitlement if bank holidays are included in the employee?s statutory minimum holiday entitlement, or if the employer grants an entitlement that exceeds the statutory minimum to its full-time workers. The fact that a part-time employee works half days is irrelevant: he or she is still entitled to a pro rata entitlement of bank holidays.
So you are entitled to 4/5ths of 8 full days (well nine this year), which works out at 6.4 days, or 7.2 this year.
To avoid treating a part-time employee less favourably than full-time employees, the employer should look at how many bank holidays the part-time employee will benefit from in light of the days of the week and hours that he or she works. If this results in a shortfall in the part-time employee?s entitlement to bank holidays, the employer should allow him or her additional holiday in lieu to take at another time. If the employee is given the time off and does not work his or her contracted half day on a bank holiday, this will count towards his or her pro rata entitlement
So you are entitled to 7.2 days bank holiday this year (your pro rata entitlement above). 7 of the 9 bank holidays that full time employees get fall on a Monday, one on a Friday, and one on a Tuesday.
SO you are getting 7x0.5 days for Mondays = 3.5
1x0.5 for the Friday =0.5
and 1 x 1 for the Tuesday = 1
that adds up to 5 days.
You are entitled to another 2.2 days off.
Make sense?