I think I know what Light Box is asking....
If you work through an agency, generally they should give you two rates.
1. A rate to work on their payroll as a PAYE contractor.
2. A rate
not to work on their payroll but through your own
LTD or an Umbrella.
If you choose the latter, the agency is saving a fair old chunk of employer's national insurance, particularly for higher paid contractors (c £250 + per day). This saving should be reflected in the
LTD / Umbrella rate because, being the employer, it'll be the
LTD / Umbrella that has to pay the employer's national insurance on the salary you receive.
This is particularly applicable if you work through an Umbrella because the contractor's gross salary is generally high (after the deduction of allowable expenses). Since a high gross salary will then attract employer's national insurance at 12.8% this can add up to hundreds per week. If the Umbrella charges £25 they're not paying it, the agency (bless them) are not paying so unfortunately Mr Contractor takes the hit.
There's no issue if the agency increases the
LTD / Umbrella rate to account for the employer's national insurance. In my experience they generally don't or they certainly don't pass on all the saving which makes for a very uncomfortable conversation between contractor and umbrella on a Friday, which starts off something like this...
"Hi Jeffery, I've checked my payslip this morning and I have a quick question......why the h3ll am I paying Employer's National Insurance?"