can i claim agency deductions as an allowable expense?

I work as a sole trader in the construction industry, and get paid through cis. i usually get my job through agencies. these agencies deduct about £20 a week from my pay, labled as "margin." this deduction is made before they take the %20 cis tax. is this an allowable expense? on an unrelated note, am i allowed to expense tool purchases made before I registered for cis and became a sole trader? and can it be from a previous tax year? the tools in question are currenty being used to carry out my work.

Hi
Yes you can claim the agency fees as expenses as they are deducting this from any pay so you would need to declare the top line income as your turnover.
For the tools, you can claim expenses in the year that they were incurred so if a previous year, you will need to amend your retrun to show this. this may give you a loss that you then carry forward into the next tax year.
Thankyou.