The five-corner model explained: will the UK use it?

A five-corner model is the familiar Peppol four-corner exchange plus a fifth corner: the tax authority. As an invoice passes between the supplier's and buyer's service providers, one or both providers also send the invoice data to a government platform. The UK is not using a five-corner model at launch in April 2029, but it is the obvious route if HMRC later wants invoice data.

Four corners first

In the four-corner model:

1. Corner 1: the supplier creates the invoice in its software.
2. Corner 2: the supplier's Access Point validates and sends it over Peppol.
3. Corner 3: the buyer's Access Point receives it.
4. Corner 4: the buyer's software imports it.

The government announced on 23 June 2026 that Peppol "will be the core interoperability network for e-invoicing in the UK", and the UK has chosen this decentralised approach. See Four-corner model explained.

Adding the fifth corner

In OpenPeppol's design for continuous transaction controls (Peppol CTC), set out in its September 2021 reference document, the sender's provider (C2) validates the invoice "in real-time, ensuring compliance with local requirements", then reports "the complete business document or a tax subset thereof (Tax Data Document or TDD)" to a Corner 5 service provider designated by the tax authority.

The reference document defines Corner 5 as "government-controlled infrastructure, which receives data from C2 and/or C3".

It describes two variants:

• Simplex: only the seller's provider reports.
• Duplex: the buyer's provider also reports receipt.

Peppol already publishes live Tax Data Document specifications. One example, for Oman, describes how an issuer's provider "creates and sends a TDD document, reporting the issued invoice" to the tax authority through its service provider.

Four vs five corners

	Four-corner	Five-corner
Invoice exchange	Provider to provider over Peppol	The same
Tax authority receives data	No	Yes, in real time or near real time
What is reported	Nothing	Full invoice or a tax data subset
Who reports	n/a	Service providers (corners 2 and/or 3)
Effect on the business	Send and receive through your provider	Largely the same; provider handles reporting
UK from April 2029	Yes	No

Where the UK stands

Confirmed:

• Decentralised model; Peppol is the core network.
• "The government will continue to explore the potential benefits of RTR but will not introduce it alongside the e-invoicing mandate in 2029." (Consultation response, 26 November 2025.)
• Any future real-time reporting "will build on e-invoicing infrastructure".

Not confirmed:

• Whether a future UK reporting system would use the Peppol five-corner model, a different data feed, or anything at all.
• Any timetable. The government said reporting would come, if at all, "once e-invoicing use was well established."

The consultation response's own glossary describes the five-corner model as "one way to incorporate RTR into a decentralised e-invoicing model". Several multinational respondents recommended Peppol "on either a four-corner or five-corner model". So the five-corner model is clearly part of the government's thinking, but it has made no decision.

Why it matters even without a decision

Choosing a decentralised Peppol network now makes a five-corner extension technically straightforward later. OpenPeppol's reference document says: "From a Tax Subject perspective, there will be limited changes and deviations between the Peppol 4-corner and Peppol CTC 5-corner models".

For UK businesses, that suggests two things:

• Little rework. If HMRC later added a fifth corner, most of the effort would fall on Access Points, not on you.
• Data quality matters now. Whatever you send over Peppol is exactly what would be reported. Errors in VAT codes or VAT numbers would become visible to HMRC.

What about cross-border trade?

The EU's VAT in the Digital Age (ViDA) package introduces digital reporting for intra-EU business supplies from 1 July 2030. OpenPeppol's CTC reference document also sets out a harmonised approach for cross-border trade. The UK is outside the EU, so ViDA's reporting does not apply to UK domestic invoices. Some EU countries' domestic systems use reporting too. See UK businesses selling to EU customers.

What to do now

• Prepare for a four-corner exchange in 2029. Do not pay for "HMRC reporting" features nobody has specified.
• Choose providers that can show they already operate where reporting exists, which suggests they could adapt.
• Read Will HMRC require real-time reporting? and the glossary entry for the five-corner model.