I'm new to CIS, I swore I'd never take on a client involved in it from either side, but here I am.
I have a new client who set up a company engaging CIS sub contractors. Later they engaged my firm and now I dig into it I discover their first sub contractor invoice (December 2017) was paid gross before they worked out what their obligations were for CIS. What is correct way to sort this out? Do we just amend the cis return (originally filed blank) and state no tax was deducted? Will that lead to penalties? Trying to claw back the cis deduction from the sub contractor now would be very difficult I imagine, and would achieve little, and my client having to gross up their cost to cover the cis deduction seems a harsh penalty.