# The four-corner model of e-invoicing explained > In the four-corner model, supplier and buyer each use their own service provider, and the providers exchange invoices over Peppol. How it works in the UK. - Canonical URL: https://einvoices.uk/news/four-corner-model-explained - Published: 20 October 2026 (2026-10-20) - Last updated: 20 October 2026 (2026-10-20) (not updated since publication) - Author: Floris Lindenaar, Editor, e-invoicing expert (https://einvoices.uk/authors/floris-lindenaar) - Publisher: einvoices.uk (https://einvoices.uk) - Type: Explainer - Topics: Four-corner model, Peppol, 2029 mandate - Language: en-GB (UK English); covers the United Kingdom ## Sources - [Tax update 2026: simplification, modernisation and fairness summary](https://www.gov.uk/government/publications/summary-of-tax-update-2026-simplification-modernisation-and-fairness/tax-update-2026-simplification-modernisation-and-fairness-summary) - [Promoting electronic invoicing across UK businesses and the public sector: consultation response](https://www.gov.uk/government/consultations/promoting-electronic-invoicing-across-uk-businesses-and-the-public-sector/outcome/promoting-electronic-invoicing-across-uk-businesses-and-the-public-sector-consultation-response) - [Peppol Network Policy v1.0.0](https://docs.peppol.eu/edelivery/policies/Peppol%20Network%20Policy%201.0.0%202026-07-02.pdf) - [About - OpenPeppol](https://peppol.org/about/) - [NHS eProcurement Strategy (Department of Health, April 2014)](https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/344574/NHS_eProcurement_Strategy.pdf) - [Peppol Message Level Status | Peppol MLS Specification](https://docs.peppol.eu/edelivery/specs/mls/v1.1.0/mls/spec/) --- The **four-corner model** is the way most modern e-invoicing networks, including Peppol, are organised. The supplier and the buyer each pick their **own** service provider, and the providers exchange invoices with each other over a common network. The UK's confirmed approach, a decentralised model with Peppol as the core interoperability network, is a four-corner model. ## The four corners | Corner | Who | Role in a UK example | |---|---|---| | **C1** | Supplier | A Sheffield engineering firm raises an invoice in its accounting software | | **C2** | Supplier's service provider (Access Point) | Validates the invoice, looks up the buyer, sends it over Peppol | | **C3** | Buyer's service provider (Access Point) | Receives the invoice, checks it, passes it on | | **C4** | Buyer | A Glasgow retailer's ERP imports the invoice for approval | The supplier never needs to know which provider the buyer uses. C2 finds out automatically by looking up the buyer's [Peppol ID](https://einvoices.uk/news/peppol-participant-id-uk) (see [SMP and SML explained](https://einvoices.uk/news/peppol-smp-sml-explained)). ## Step by step 1. **C1 creates** a structured invoice, for example Peppol BIS Billing 3.0 in UBL XML. It is not a PDF. 2. **C2 validates** it against the rules and rejects it if it fails. 3. **C2 looks up** the buyer's Peppol ID to find C3's address and certificate. 4. **C2 sends** the invoice securely to C3 using the AS4 protocol. 5. **C3 checks** it and delivers it to C4. If something fails, C3 sends a Message Level Status back to C2 (see [Invoice Response vs MLR/MLS](https://einvoices.uk/news/peppol-invoice-response-message-level-response)). 6. **C4 processes** the invoice, ideally matching it to the order automatically. On Peppol, C2 and C3 have both signed the same Peppol agreements and passed conformance testing, which is what lets strangers trust each other. ## Why four corners and not one platform? The Department of Health's NHS eProcurement Strategy (April 2014), which brought Peppol into the NHS, explained the model simply: - "each NHS provider selects its own access point for messaging all suppliers" - "each supplier selects its own access point for messaging all NHS Providers" - "There are no fees payable between access points, with each party paying only their own PEPPOL access point provider." Compared with alternatives: | Model | How it works | Main drawback | |---|---|---| | Two-corner (direct) | Supplier connects straight to buyer, by EDI link, portal upload or email | One connection per trading partner | | Three-corner | One platform serves both sides | Everyone must join the same platform; risk of lock-in | | **Four-corner** | Each side chooses a provider, and providers interconnect | Needs common rules and governance (Peppol supplies these) | | Five-corner | Four-corner plus reporting to the tax authority | More data flows and obligations | | Centralised / clearance | Invoices pass through a government platform | Dependence on one platform; heavier state role | OpenPeppol contrasts its approach with "closed or 'three-corner' networks". The four-corner model's selling point is that, like email, one connection reaches everyone. ## Four corners vs five corners In a **five-corner** model, invoice data is also sent to the tax authority, the fifth corner, usually by the service providers. The Peppol Network Policy treats a five-corner model as "a combination of multiple instances of a 4-Corner Model". Technically, the fifth corner is another Peppol exchange. In the government's 2025 consultation response, several respondents recommended "considering the Peppol network on either a four-corner or five-corner model". The government's decision for launch: **no real-time reporting alongside the mandate.** So the UK starts as a four-corner model. Whether a reporting element (a fifth corner) is added later has not been confirmed. See [Five-corner model and the UK](https://einvoices.uk/news/five-corner-model-uk) and [Will HMRC require real-time reporting?](https://einvoices.uk/news/real-time-reporting-uk) ## What it means for different businesses - **Small businesses:** you will usually get corner 2 or 3 through your accounting software. You do not need to "join" Peppol separately. See the [small business guide](https://einvoices.uk/news/e-invoicing-small-business-guide). - **Larger businesses:** you may connect your ERP to a provider by API or file transfer. Pick the provider on certification, validation, portability and price (see [How to choose a Peppol Access Point](https://einvoices.uk/news/how-to-choose-a-peppol-access-point)). - **Public sector suppliers:** many NHS suppliers already work this way. - **Businesses that receive invoices on supplier portals:** the four-corner model can replace dozens of portal logins with one connection, if your customers support it. ## What is confirmed and what is not **CONFIRMED (official):** - Peppol "will be the core interoperability network for e-invoicing in the UK" (GOV.UK Tax Update summary, 23 June 2026). - Decentralised model, with mandatory e-invoicing for B2B and B2G VAT invoices from April 2029. - No real-time reporting at launch. **NOT YET CONFIRMED (as of 20 October 2026):** - how service providers will be accredited for the UK mandate - what role, if any, non-Peppol channels such as existing EDI or legacy systems will have. The government says it "will continue to engage with stakeholders regarding the role of legacy systems which cannot interoperate in the future system". - whether and when any reporting to HMRC (a fifth corner) will follow The implementation roadmap is due at Budget 2026 on 28 October. ## What to do now 1. Identify your corner 2 and 3. Ask your software vendor which certified Peppol provider it uses. 2. Check that your provider can both **send and receive**. 3. Find your main customers' and suppliers' Peppol IDs in the [Peppol Directory](https://einvoices.uk/news/peppol-directory-lookup-uk). 4. Read [What is Peppol?](https://einvoices.uk/news/what-is-peppol) and the glossary entry for the [four-corner model](https://einvoices.uk/news/four-corner-model-explained). ## Frequently asked questions ### What is the four-corner model? It is an e-invoicing model where the supplier (corner 1) and buyer (corner 4) each use their own service provider (corners 2 and 3). The providers exchange invoices over a shared network such as Peppol, so neither business needs to use the other's provider. ### Will the UK use the four-corner model? The UK has confirmed a decentralised model with Peppol as the core interoperability network, which works on the four-corner model. There will be no real-time reporting to HMRC at launch. ### What is the difference between the four-corner and five-corner model? In a five-corner model, invoice data is also reported to the tax authority, the fifth corner, usually by the service providers. The UK has said real-time reporting will not be introduced alongside the 2029 mandate. ### What is a three-corner model? A single provider or platform serves both supplier and buyer, as in many closed supplier portals. It works only if both sides join that platform. ### Who pays in the four-corner model? Each business pays only its own provider. There are no fees between Access Points on Peppol. --- How to cite: "The four-corner model of e-invoicing explained", einvoices.uk, 20 October 2026, https://einvoices.uk/news/four-corner-model-explained einvoices.uk is an independent publication and is not affiliated with HMRC or the UK Government. Nothing here is tax advice; check the sources and official GOV.UK guidance before acting.