A written record of what your system does
Its rules and dependencies, each linked back to the source code.
Your most important system is often the one nobody wants to change.
It was written decades ago, in COBOL, PL/I, Fortran or another language few people still write. It is expensive to run and hard to change. The people who built it have retired or left, and the documents no longer match what it actually does.
You rely on it every day, so you cannot turn it off. It gets harder and more expensive to keep running every year. And if a new system gets even one rule wrong, your customers feel it.
Replacing an old system should not put your business at risk.
When a replacement goes wrong, everyone sees it.
£48.65 millionthe fine after one platform switch
In April 2018 TSB moved its customers onto a new banking platform. It failed on the day, and a large share of its 5.2 million customers were affected. The regulators later fined TSB £48.65 million, and the former chief information officer was fined personally.
FCA and Bank of England, 2022 and 2023. FCA notice, Bank of England notice, PRA decision.
Sovereign finds every difference before you switch.
Who it is for
For organisations that cannot switch their systems off.
Retail and distribution
Stock, order and warehouse systems on older midrange computers.
Manufacturing and logistics
Production, stock and delivery systems that run every shift and were built decades ago.
Central and local government
Tax, benefits and licensing systems that depend on older code and fewer people who know it.
Healthcare
Patient administration and hospital systems that cannot go offline.
Energy and utilities
Billing, metering and asset systems that serve whole regions.
Telecoms and transport
Billing, scheduling and network systems built decades ago.
Banks, insurers and pensions
Core banking, policy and pension systems running on decades-old mainframe code.
Defence and national infrastructure
Systems that must be modernised inside sealed, secure networks.
After Sovereign
What you get with Sovereign.
- A modern system your team can understand and change.
- The rules your business runs on, finally written down.
- Proof that the new system works, before you switch.
- Lower running costs, and no dependence on people who are about to retire.
A worked example
A public mainframe credit card application.
- Programs
- 44
- Shared definitions
- 62
- Batch jobs
- 55
We gave Sovereign the source code of a public mainframe credit card application. It mapped all 44 programs, 62 shared data definitions and 55 batch jobs, and found a missing file before any rebuilding started. Sovereign rebuilds and proves COBOL, PL/I, JCL, Fortran, MUMPS, REXX, Perl and ColdFusion, each checked against its own compiler or interpreter.
Then the proof report: every match and every difference.
Old and new run on the same inputs. Each case lights up as it matches. When one differs, the report shows the cause, the fix and the re-run, with the evidence kept for your team.
Proof reportAccount posting, part 1 of 5
8 cases run8 match1 difference, resolved
- Statement, balance in creditInterest 3.13, fee 0.00Interest 3.13, fee 0.00MatchDiffers
- Statement, overdrawnStatus OD, charge 15.00Status OD, charge 15.00MatchDiffers
- Payment 31 days lateLate fee 12.50Late fee 12.50MatchDiffers
- Interest on 375.004.69 (rounded)
4.68754.69 (rounded)MatchDiffersCause The old program rounds interest to pence (COMPUTE ROUNDED, ACCTPOST lines 8 to 9). The new system did not.Action Rounding added. Case re-run and matched. Inputs, both outputs and the source lines are kept for your team. - Overdrawn and lateFee 27.50Fee 27.50MatchDiffers
- Zero balanceInterest 0.00, fee 0.00Interest 0.00, fee 0.00MatchDiffers
- Month end, 2,400 accountsPosted 2,400Posted 2,400MatchDiffers
- Leap day statementInterest 1.25Interest 1.25MatchDiffers
The Sovereign method
Read. Rebuild. Prove. Switch over.
- 1
Read
We work out exactly what your system does: its rules, data and dependencies. Each rule points back to the lines of code it came from, so your team can check it.
- 2
Rebuild
We build the modern replacement from that record.
- 3
Prove
We run old and new on the same inputs and show you every match and every difference, until the report is clean.
- 4
Switch over
When a part is proven, the new system takes over its work in small steps while the old one stays ready. If results drift, the work goes straight back to the old system. You approve every step.
Where it runs
Runs inside your network. Your code stays with you.
- 01
Installed on your site
Sovereign comes as a sealed package that installs on a machine inside your own network.
- 02
No internet needed
It is built to run with no internet connection, including in air-gapped sites. Reading, rebuilding and proving do not need any outside service.
- 03
No AI
Reading, rebuilding and proving use no AI model, so every result is exact and repeatable. Nothing leaves your network without your say.
Our promises
Our promises to you.
- Your current system keeps running until the evidence says the new one matches.
- We replace one part at a time, never the whole system at once.
- Each step is scoped and priced on its own. You decide the next step after you see the result.
- Your code and data stay under your control. We agree secure access before you share anything.
- You see every difference and every open question before anything goes live.
- You keep the reports and the evidence, and your team can re-run the proof themselves.
What you receive
Three things, all yours to keep.
The new system
Modern code for the agreed part, built from the record.
The proof report
What matched, what differed, what is still open, and instructions to re-run it.
How to start
Step 1 · Recommended first step
Start with an Assessment.
Before anything changes, we map your system: what you have, what it depends on, and where to start. Scope agreed in writing before we begin.
- InventoryEvery program, data definition and batch job, and anything missing.
- RoadmapWhich parts to move first, and in what order.
- Risk registerEach risk linked to the file and line it comes from.
- ReadinessWhich parts are ready to rebuild and prove, and what the rest need.
- ReviewChecked and signed off by an analyst before you receive it.
- Week 1Read the part and write down its rules. You check the record.
- Weeks 2 to 3Rebuild it from the record.
- Week 4Run old and new on the same inputs. You receive the proof report.
Is Sovereign right for you?
What we need from you
The old system able to run, representative test cases, and one person who owns the decision.
For each person in the decision
- Technology leaderSovereign works alongside your estate. It reads the source you have, runs where you say, and hands your team code they can maintain. No platform to adopt.
- SecurityAccess is agreed in writing before anything is shared: named people, your environment or a sealed one, and access that ends with the work.
- Finance and procurementFixed scope, fixed price, stage by stage. Each step is agreed before it starts, and the next step is your decision after you see the result.
- Risk and auditThe proof report shows every match and difference with its inputs and source references. Your team can re-run it without us.
Questions we are asked first.
How long does a pilot take?
Two to four weeks for one part of your system, once access is ready.
What happens when old and new differ?
Every difference is shown to you with the inputs that caused it and the lines of old code behind it. Some differences are faults in the old system that you choose to keep or fix. Some are gaps in the new one. You decide which, and the proof is re-run until the report is clean.
What if the old system cannot be run?
We agree with you how each part will be proven before the pilot starts.
Where does our code go, and who can see it?
Where you say. We agree secure access in writing before you share anything: your environment or a sealed one we set up, named people only, and access that ends when the work ends.
Who owns what at the end?
You do. The written record, the new code and the proof report are yours, and your team can re-run the proof without us.
How is it priced?
Each step is fixed in scope and agreed in writing before work starts. Price is set out in the written scope, so there are no surprises later.
Tell us about the system you need to replace.
Email us about the system and what worries you about changing it. We reply with a proposed first step.