Howdy iron_lady,
If you were a permanent employee your employer would make an allowance for the amount they have to pay in
NI contributions... so they say you're on £30,000 but they've already budgeted for the employers'
NI on top.
Someone has to pay it and in an umbrella company that's you... unless you want to ask them to up their fee and not charge you
NI... or lower your rate to account for the employers'
NI.... but the net result would be the same to you.