Bank holiday entitlement working average 32 hours weekly?

I work 30 hours a week tuesday to friday inclusive, and approx, every 2 saturdays mornings per five. I am told that I am not entitled to any time off in lieu of the bank holidays that happen to be my 'day off', as these are down to 'employer's discretion' (or meanness!). Am I being told porkies, I don't like rocking the boat, and most people including my employers know this, so I feel my good nature is being milked here? Thanks in advance.