From links to liberty: the hidden rulebook behind SJP imprisonment
An FOIA disclosure reveals how imprisonment for unpaid Single Justice Procedure fines is determined in practice
I recently published an article — MoJ FOIA: not quite proof, not quite vibes — giving a forensic breakdown of a Ministry of Justice response to a Freedom of Information Act request.
The subject may seem arcane: imprisonment for non-payment of fines under the Single Justice Procedure. The principle is not. Deprivation of liberty within a high-volume, largely automated pipeline raises an obvious concern — “jail by algorithm.”
The Ministry’s response sharpened that concern rather than resolving it. It confirmed that it holds no data on how often this pipeline leads to custody. That is not a marginal omission. It is a governance and accountability gap at the core of the highest-volume criminal process in England and Wales.
As part of that response, the Ministry pointed to internal guidance documents — but did not supply them. Instead, it provided intranet links I could not access. The existence of the material was acknowledged; its content remained out of reach.
That is a familiar pattern: disclosure in form, not in substance.
What followed was more constructive. In response to the confusion over those links, the Ministry issued a separate FOIA response of its own initiative, this time attaching the documents in full.
The result is disclosure of three files:
Calculating Terms in Default
Partial Commitment
Fine Days in Default Calculator
What emerges is not a single, clear legal rule, but something more revealing: an operational system sitting beneath the statute — a layer of guidance, tables, and tools that actually guides how financial penalties are converted into days in custody.
And that system is not by default visible to the public.
The core revelation — law vs system
On paper, imprisonment for non-payment of fines is governed by statute — primarily the Magistrates’ Courts Act 1980.
In practice, the disclosed material shows a three-layer system:
statute
internal guidance
a table and calculator
The statute provides the outer frame. The guidance interprets it. But the outcome — the number of days in custody — is produced at the bottom layer.
That is the critical point.
The duration of imprisonment is not determined directly by statute, except as a hard limit. It is determined operationally, by reference to a table and implemented through a calculator.
The law describes the system.
The tool in effect fixes the number in practice.
The untraceable table
At the centre of this system sits a table — implemented in practice via a spreadsheet calculator — used to convert a monetary sum into a number of days in custody. It has been in use across the courts for around twenty years. Yet, according to the Ministry’s own material, its origin cannot be traced.
There is no cited statutory source, no formal instrument, and no identifiable author. It does not appear in legislation. It is not clearly anchored in any publicly accountable legal framework. And yet it performs a critical function: it plays a central role in determining how long a person may be deprived of their liberty.
That is the uncomfortable reality. A core mechanism of the system — one that translates debt into detention — operates without clear legal provenance.
Not enacted, not explained, and not traceable.
Just applied.
What legally authorises imprisonment?
The Ministry of Justice states, in response to the FOIA request, that committal to custody is a “fresh judicial determination”.
The internal guidance points in a different direction. It frames enforcement as arising from a “sum adjudged to be paid” by the original conviction — a single, indivisible financial liability carried forward into enforcement.
These are not obviously the same thing:
One describes a new judicial act, made at the point of committal.
The other describes the execution of an existing one, flowing from the original conviction.
The system appears to rely on both descriptions at once.
That creates a problem. When the state deprives someone of their liberty, the legal basis for doing so should be clear, stable, and intelligible. Here, it is not presented as a single, coherent foundation, but as overlapping rationales drawn from different layers of the system.
The result is not outright contradiction, but something arguably just as concerning: ambiguity at the point where clarity matters most.
The accountability gap
Alongside the legal ambiguity sits a more practical problem: the system cannot account for its own outcomes at a central level.
The Ministry of Justice confirmed that it does not hold data on how many individuals are committed to custody for non-payment of fines imposed under the Single Justice Procedure. To obtain that information, it says, would require manual inspection of individual case files.
This is striking.
The Single Justice Procedure is not a niche process. It is the highest-volume criminal pipeline in England and Wales, handling millions of cases. Imprisonment is a recognised enforcement outcome within that system.
Yet there is no central visibility on how often that outcome occurs.
The system operates at scale. But when it comes to one of its most serious consequences — the deprivation of liberty — it cannot readily say how often it is used.
That is not just a data gap. It is an accountability gap.
Synthesis
Taken together, these documents do not resolve the questions raised by the original FOIA response. They sharpen them.
They show that the conversion of financial penalties into custodial time is not expressed as a single, clearly articulated rule, but is instead mediated through a combination of guidance and tooling.
The statute defines the legal framework. But the mechanism that produces the outcome — the number of days in custody — is implemented elsewhere, using instruments that are not themselves statutory, not formally documented, and not ordinarily visible.
This is the point at which abstraction becomes consequence.
The law provides the authority. But it is the machinery around it that determines how that authority is exercised in practice — and, ultimately, how long someone is deprived of their liberty.
Other matters worth noting (beyond scope)
The disclosed material also contains a number of additional features that reinforce the same underlying pattern, but sit outside the core issue.
Multiple financial penalties are consolidated into a single enforceable sum at the point of enforcement
“Partial commitment” — splitting enforcement across components — is expressly ruled out
Procedural workarounds are used at the point of sentencing to manage edge cases
Elements that are not independently imprisonable (such as the surcharge) are included in the total sum used to calculate custody
The system is operationally mediated through legal advisers rather than judges
A calculator is used to convert monetary amounts into days in custody — in effect, an algorithmic translation of debt into detention
Each of these points warrants closer examination in its own right.
Taken together, they reinforce the same conclusion:
The system operates through internal logic and tooling
that sit beneath, and extend beyond, the statute itself.
Closing
These documents expose not a single defect, but a structural condition.
The legal basis for imprisonment is not expressed as a single, clear foundation, but as overlapping interpretations. The mechanism that determines duration relies on a table whose origin cannot be traced. And the system as a whole operates without central visibility over how often it results in custody.
Individually, each of these points might be explained away. Taken together, they describe something more serious:
a system in which the deprivation of liberty is mediated by layers of practice that are not fully anchored in statute, not fully documented, and not fully overseen.
The law describes the system. But it is the hidden machinery that decides how long someone is locked up.