Two different questions hide inside this one, and conflating them causes most of the confusion.
Is it a valid invoice? — a fairly low bar, and largely a matter of commercial law.
Is it a valid VAT invoice? — a much higher bar, and the one that decides whether you can reclaim the VAT.
You can hold a perfectly legitimate invoice that doesn't support a VAT reclaim. That's the case worth being able to spot.
What a VAT invoice needs
Requirements vary by jurisdiction, and the UK list is broadly representative of the EU pattern:
- A unique sequential number
- The supplier's name and address
- The supplier's VAT registration number
- The date of issue, and the tax point where different
- The customer's name and address
- A description of the goods or services
- For each rate: the quantity, unit price, rate and net amount
- The total net, the VAT amount, and the gross
- Any discount applied
Miss the VAT number or the sequential number and it isn't a valid VAT invoice, whatever else is on it. This is one of the arguments for structured e-invoice formats, where the required fields are part of the schema rather than a layout choice.
Simplified invoices
Below a threshold — £250 including VAT in the UK — a simplified invoice is acceptable, and needs much less:
- Supplier name and address
- Supplier VAT number
- Date
- Description
- The rate applied and the gross amount
No customer details, no separate VAT figure. This is why a petrol receipt is a valid VAT document and a £4,000 invoice in the same format is not.
Above the threshold, the full list applies.
Documents that look like invoices and aren't
The four that get entered by mistake:
Pro-forma invoices. A quote wearing an invoice's clothes. Not a demand for payment, not a VAT invoice, and entering one creates a liability that doesn't exist. Usually marked "pro-forma", though not always prominently.
Statements. A summary of invoices already issued. Entering one double-counts everything on it, and it's the single most common entry error in a purchase ledger.
Order acknowledgements and delivery notes. Sometimes carry prices, which is what makes them dangerous.
Receipts. Proof of payment, not a demand for it. Fine as a VAT document if it carries the simplified fields; not something to enter as a payable.
A quick test that catches most of these: does it demand payment, and does it have its own unique number? A statement has neither. A pro-forma has the second but not the first.
When something's missing
No VAT number, and you need to reclaim. Ask for a corrected invoice. Don't reclaim on the basis of one that doesn't qualify — this is exactly what a VAT inspection looks at.
Wrong customer name. Addressed to a person rather than the company, or to a trading name that isn't the legal entity. Worth correcting on anything material.
No invoice number. More common than you'd expect from small suppliers and sole traders, and it makes duplicate detection impossible.
Missing description. "Services rendered" for £8,000 is not a description. It's also the shape a fraudulent invoice takes, which is why it's worth querying rather than accepting.
Suppliers are generally fine about reissuing. The awkwardness of asking is much smaller than the awkwardness of a disallowed reclaim.
Digital and e-invoices
A digital copy is as valid as paper in most jurisdictions, provided it's complete, legible, unaltered and retained for the full period.
Structured e-invoices — Factur-X, UBL, ZUGFeRD — carry the same requirements. The catch is that a file can be technically valid and nearly empty: a Factur-X file at MINIMUM profile contains totals and identifiers and no line items at all. Valid as a file, thin as a record.
A practical check
Rather than the full list every time, three questions catch nearly everything:
- Does it demand payment, with its own unique number? If not, it isn't an invoice.
- If you're reclaiming VAT, is the supplier's VAT number on it? If not, ask.
- Is the description specific enough that someone in two years could tell what it was for? If not, ask now rather than at year end.
Cribble reads the fields that decide this — supplier, VAT number, invoice number, tax rates, line detail — and scores each one separately, so a missing or uncertain field is visible before the invoice is posted rather than at the VAT return.