If you work for 2 Agencies on paye do you get taxed more 
Is it classed as a second job and a higher percent of Tax
it does not get taxed at higher rate
have the agency that gives you the most work as main employer
they will use your tax code and give you the allowances that are entitled
the other other agency will tax you at BR which means you pay tax on all your income
over a year it will work out about right
next May when you get P60 check income and tax
if you have overpaid
ask inland revenue for refund