Technical Design Authority (TDA)

The TDA is Defra's technical decision-making authority. It agrees roadmaps, grants authority to solution design authorities, and reviews cross-cutting and novel work and exceptions to the guardrails. It is a peer review that helps teams get to a good design - not an exam.

Draft - to be confirmed

Parts of this page, such as names, timings and thresholds, are still being confirmed by the architecture team. Use it as a guide, and check with your solution design authority before relying on the detail.

When to come to the TDA

Use which route do I take?. In short, come to the TDA when your work:

• is novel for Defra - new technology, pattern or use of AI
• is cross-cutting - other services, teams or arm's length bodies will depend on it or be affected by it
• needs an exception to a Must guardrail
• fills a gap in the technology capabilities
• is escalated by a solution design authority

Come early. The best time is the end of discovery or early alpha, when changing direction is cheap. You can come more than once.

What the TDA does

• Reviews designs and gives clear, actionable outcomes
• Approves or declines time-limited exceptions to Must guardrails
• Identifies reuse opportunities between teams
• Feeds lessons into the guardrails and handrail
• Recommends items to the TGB

Membership

Chaired by the Chief Architect or a delegate, with enterprise, solution, data and security architects, platform representatives and, for relevant items, arm's length body architects. Delivery partners presenting on behalf of a Defra team are welcome to attend.

How it works

Step	What happens	Timing
1. Talk to us	An informal conversation with an architect to shape the submission	Any time
2. Submit	Complete the TDA submission template and email it with any ADRs and diagrams - see raise a decision for review	5 working days before the meeting
3. Review	30-minute slot: 10 minutes to present, 20 minutes discussion	Fortnightly
4. Outcome	Recorded in the architecture decision register and shared within 3 working days

Outcomes

Outcome	Means
Endorsed	Proceed.
Endorsed with conditions	Proceed, meeting named conditions by a named date.
Not endorsed	Rework and come back. The TDA explains why and offers support.
Escalated	The decision needs the TGB.

What good looks like in a submission

• The problem and outcome in plain English, and the business capabilities affected
• The options considered, including the strategic options from the handrail, and why you prefer one
• A context diagram and a container-level diagram (the C4 model works well)
• Which guardrails you meet and which you do not
• Risks, including security (a current threat model) and data protection
• What you need from the TDA - a decision, advice or an exception

Short is better. Five pages is plenty.