That one answer decides most of it — whether you are inside CIS, whether the reverse charge applies, whether you are a contractor as well as a subcontractor, and where your cash is going. Send it over and we will tell you what is wrong before you decide anything.

Your last three CIS returns if you pay subcontractors, and your payment and deduction statements if you are paid under deduction. Bank statements are not a substitute — the statements are the evidence.
Materials that never reduced a deduction, travel that should not have been in the base, a verification reference missing from a higher-rate statement, returns filed after the 19th, deductions paid after the 22nd. And whether you would pass the turnover test for gross payment status.
A fixed monthly fee, quoted after the review and agreed before anything starts. If the answer is that your paperwork is fine, we will say so.
Before you send anything
The free review is only as good as what it has to look at, and the single most useful thing you can send is the documents rather than a description. Three months is enough to see a pattern and short enough that you can find it.
If you are paid under deduction, send your payment and deduction statements. Not bank statements — the deduction statements. They are the evidence of what was taken and on what basis, they carry the verification reference where a higher-rate deduction was made, and they show the materials figure that reduced the deduction. A bank receipt shows a net number and nothing else, which is why so many businesses have never established whether their materials were treated correctly.
If you pay subcontractors, send the last three monthly returns and a couple of the invoices behind them. What we are looking at is whether the materials figures look reasonable, whether travel and subsistence have been correctly left inside the deduction base, whether verification references are being recorded with their letter suffixes, and whether the returns and the payments went in on the 19th and the 22nd rather than whenever the month got busy.
If you are both, which most trade businesses of any size are, send both. The two positions interact: the CIS you deduct from your own subcontractors is one of the four things a company can offset its own suffered deductions against.
There is no charge for the review and no obligation at the end of it. If you want us after that, the fee is fixed, monthly, quoted on what we have just seen, and agreed before anything starts.
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