Commercial & Contract · Mandatory · Pre-Construction

Subcontractor Order and Purchase Order

A formal purchase order placed with a subcontractor or supplier.

Last reviewed: 29 March 2026 — This guide reflects UK law as of this date. Contract Law remains current with no amendments enacted as of 29 March 2026. Next scheduled review: 29 March 2027.

Legal basis	Contract Law — offer, acceptance, consideration, and intention to create legal relations
Order vs agreement	The subcontract agreement establishes the legal relationship and terms; the subcontractor order (or purchase order) activates that agreement for specific works or materials on a specific project
Supply chain management	Every subcontractor and supplier must receive a formal written order before any work begins or materials are delivered — no exceptions
Purchase orders	A purchase order is used for the supply of materials or goods. It specifies quantity, specification, delivery date, and price. The supplier's acceptance of the PO creates a binding contract for the supply of those goods.

1. The Order — Formalising Every Appointment

The subcontractor order is the formal instruction that activates a subcontract agreement for specific works on a specific project. Without a written order, there is no clear record of what was instructed, when it was instructed, or on what terms. In the event of a dispute — over scope, price, programme, or quality — the order is the document that both parties will rely upon to establish what was agreed. An order is not bureaucracy; it is the commercial foundation of every subcontract appointment.

The distinction between a subcontractor order and a purchase order is important. A subcontractor order instructs specific works — labour, plant, and materials to carry out defined construction activities on site. A purchase order instructs the supply of materials or goods only — bricks, steel, timber, sanitary ware, or any other product required for the works. Both require formal written orders before the subcontractor mobilises or the supplier delivers. The principal contractor's supply chain management depends on every appointment being formally ordered, tracked, and managed through to completion.

An order management system eliminates the gaps that cause disputes

A centralised order management system ensures that every subcontractor and supplier order is issued, numbered, tracked, and linked to the relevant subcontract agreement. It provides a clear audit trail from order through to final account. Without it, orders are issued informally by email or verbally, creating scope gaps, duplicate orders, and commercial exposure that only surfaces when it is too late to resolve easily.

2. Subcontractor Order — Content

Field	Detail
Order number	Unique sequential reference. Links to financial and contract management systems. Every order must have a unique number for tracking and audit purposes.
To	Full legal name and registered address of the subcontractor or supplier receiving the order.
From	Full legal name of the principal contractor or employer issuing the order. Authorised signatory details.
Project	Project name, site address, and project reference number. Ensures the order is unambiguously linked to the correct project.
Description of works	Precise description of the works or materials being ordered. Reference to drawings, specifications, schedules, and bill of quantities items where applicable. Scope clarity prevents disputes.
Order value	Total value of the order — fixed price, schedule of rates, or remeasurable. Must state whether the value includes or excludes VAT. Currency (£ sterling).
Start date	The date on which the subcontractor is required to commence the ordered works on site, or the date by which materials must be delivered.
Completion date	The date by which the ordered works must be completed, or the final delivery date for materials. Programme obligations and liquidated damages provisions apply from this date.
Conditions of order	Reference to the applicable subcontract agreement, standard form (JCT, NEC), and any bespoke conditions. The order incorporates the terms of the underlying agreement.
Authorised by	Name, position, and signature of the person authorised to issue the order on behalf of the principal contractor. Only authorised persons should issue orders — unauthorised orders create commercial exposure.

3. Common Mistakes

Starting work before a formal order is issued

This is the single most common and most damaging mistake in subcontract management. When work starts without a formal order, there is no written record of scope, price, programme, or conditions. The subcontractor may proceed on the basis of verbal discussions, email exchanges, or assumptions — none of which provide the contractual certainty needed to manage the works. Disputes over what was agreed become impossible to resolve cleanly. Every subcontractor and supplier must have a formal written order in hand before any work begins or any materials are delivered.

4. Frequently Asked Questions

What is the difference between a subcontract agreement and a purchase order?▾

A subcontract agreement is the overarching legal contract that establishes the relationship between the principal contractor and the subcontractor — it sets out the terms and conditions, payment provisions, dispute resolution mechanisms, insurance requirements, and all other contractual obligations. A purchase order (or subcontractor order) is the specific instruction issued under that agreement for a defined scope of works or supply of materials on a particular project. The agreement governs the relationship; the order activates it for specific works. A subcontractor may have one agreement but receive multiple orders under it across different projects or phases.

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