I have a friend who works job share, she does all day monday, tuesday and wednesday mornings. Her employers are now sayin that she must use her own holiday to cover bank holidays or take them without pay...this is not a small company this is a large national company emplying many people. Her office/company will be closed on bank holidays so it's not like she can offer to work them...can they do this?

This should help you CLICK Good luck !

I think it depends on your contract - I've worked in places where you had 20 days holiday including the Bank Holidays

I'm pretty sure they can do this, especially with job shares. Main thing is to see what is in her contract of employment. Its not uncommon for local bosses to make up rules as they go along.

Usual practice (though not compulsory) is for both job share employees to get a pro-rata addition to their leave allowance to cover bank holidays, so a three day worker would get say an additional 5 days and a two day worker would get say 3 additional days holiday.

Acas are the people for employment advice CLICKY

If you're an employee and not a member of a union, its very hard not to be walked on whenever management choose.

Whether she is part time or full time she still has the same rights. Check out her Contract of Employment, if there is no provision for this, put in a Grievance. When you put in a grievance, you have the right to be accompanied. If she are in a union, see her steward

As far as I know it's normal practice to pro-rata bank holidays for part time staff. Even the NHS do it and they're the 3rd biggest employer in the world.
Because of this last Labour government increased the legal minimum number of days leave to 28 days. However, this can include the 8 days bank holiday entitlement.

Thanks Pob am showing my age there are't I!