Quick answer
Liability after a UK road traffic collision is decided on evidence, not on the strength of either driver's account of events. The third-party insurer reaches a liability decision by weighing seven distinct streams of evidence: contemporaneous photographs, dashcam footage, third-party CCTV, signal and ANPR data held by the highway authority, witness statements, the police record, and the engineer's report on damage patterns. Most of these streams have a retention window - sometimes as short as 14 days. After that window the evidence is gone.
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How to gather and preserve evidence after a UK road traffic collision
Liability after a UK road traffic collision is decided on evidence, not on the strength of either driver's account of events. The third-party insurer reaches a liability decision by weighing seven distinct streams of evidence: contemporaneous photographs, dashcam footage, third-party CCTV, signal and ANPR data held by the highway authority, witness statements, the police record, and the engineer's report on damage patterns. Most of these streams have a retention window - sometimes as short as 14 days. After that window the evidence is gone.
This guide explains each stream, who holds it, the typical retention window, and what a non-fault claimant should be doing within the first 24 to 72 hours to preserve every stream that might bear on liability.
1. Contemporaneous photographs - your most reliable evidence
Photographs taken at the scene by the parties themselves are the single most reliable form of accident evidence because they capture facts that no later inspection can reconstruct: the resting positions of the vehicles, the debris field, the road surface, the signage, the lighting state and the weather. They also pin the time of the incident through camera EXIF metadata.
Take wide-angle context shots first, then close-ups, then specific elements: signage, lane markings, traffic light state, skid marks, and any temporary works or obstructions. Photograph the third-party plate clearly. Where injuries have occurred and it is appropriate, photograph any visible injuries (with the injured person's consent). Back up the originals to cloud storage the same day; do not crop, edit or run them through filters.
DETAIL
Section 3 of the walkthrough.
2. Dashcam footage - yours and the other driver's
If you have a dashcam, the first job is to preserve the file. Most dashcams record on a loop and overwrite older footage within hours or days, so the relevant clip must be moved to a memory card or laptop immediately. Save the file with the date, time and a short description in the filename and back it up to cloud storage. Note the dashcam make, model and firmware version: insurer engineers may want this.
Where the third-party driver had a dashcam too, ask for the clip at the scene if it is safe and reasonable to do so. Where they refuse, the third-party insurer can still be asked to disclose the footage through the pre-action protocol, but disclosure on a voluntary basis at the scene is faster and cheaper than disclosure several months later.
3. Third-party CCTV and bus-cam - the 14 to 31 day retention window
Public CCTV networks operated by London boroughs, Transport for London, county councils and shopping centres have retention windows that vary from 14 days to 31 days. Most metropolitan councils retain for 28 days. The CCTV is usually held on a circular buffer; once the buffer is full, the oldest footage is overwritten with no recovery option.
To preserve council CCTV, write to the council's Information Governance team within the first 72 hours quoting the date, time, location and direction of the collision. To preserve TfL bus-cam footage, write to TfL's Information Access team within the same window - every London bus has internal and forward-facing cameras and the route, run number and stop times are recorded. To preserve shopfront or petrol-station CCTV, ask politely on the day; many operators will hold a clip on request before the routine retention deletion runs.
4. Signal phase, ANPR and traffic-survey data
Where a collision happens at a signalised junction, the phase of the lights at the moment of impact is often the most important fact for liability. Signal data is held by the highway authority - Transport for London for the TfL Road Network in London, the borough council for council-managed roads, and National Highways for motorways and trunk roads outside London.
Signal data is typically held for 28 to 90 days depending on the system. ANPR records (kept for traffic-management or restricted-zone enforcement, not policing) can also place a vehicle on a particular road at a particular time and corroborate the photographic record. Disclosure requests should specify the junction, the date, the time window and the direction of travel.
5. Witness statements - record what was said while it is fresh
Witness recollections degrade fast and the contact details on a hastily-scribbled note often go missing. Within 24 hours, contact every witness who gave you their details and ask whether they would be willing to give a short written statement of what they saw. The statement does not need to be a formal Civil Procedure Rules statement of truth; a clear, dated description of what they observed is sufficient at this stage.
Where a bus, taxi or commercial driver was a witness, the operator's name plus the route, badge or vehicle number is usually enough to allow a later trace through the operator. Independent witnesses to a road traffic collision are frequently decisive, particularly where signal phase or speed is in dispute and no objective camera footage survives.
6. The police record - CAD, CRIS or online collision reporting reference
Where the police attended the scene, a Computer Aided Dispatch (CAD) reference is generated from the 999 call. Where a crime or reportable incident is recorded, a CRIS (Crime Report Information System) reference follows. Where you reported online to the Met Police MPS Collision Reporting Service or the equivalent for another force, a unique reference is issued by the system.
Quote whichever reference you have in every subsequent letter to the third-party insurer and in any pre-action protocol correspondence. Police accident reports themselves (the MG-NFA or MG-11 statement) are usually only released through a formal disclosure request and may not be available until any criminal proceedings have concluded; for property-damage claims the insurer can sometimes obtain a redacted summary direct.
7. The independent engineer's report
The damage pattern on the vehicles is itself evidence. An independent engineer's inspection - usually arranged by the accident management partner, not the at-fault insurer - establishes the repair scope, the like-for-like vehicle classification for credit hire, and any pre-existing damage that the at-fault insurer might otherwise try to attribute to the collision. The report typically becomes the spine of the claim file and the basis for the engineer-to-engineer negotiation that fixes the repair quantum.
Critically, the inspection should happen before any repair work is started. Repairing the vehicle first removes the most direct evidence of the impact pattern, which is exactly the evidence the third-party insurer's engineer is going to look at. We cover this in detail in the dedicated post on engineer inspections.
DETAIL
Section 9 of the walkthrough.
8. Putting it together - a 72-hour evidence sprint
The discipline that wins liability disputes is to treat the first 72 hours as an evidence sprint. Day one: photograph everything at the scene; preserve dashcam files; exchange details; report to the police if reportable; call your accident management partner. Day two: contact witnesses for short written statements; lodge CCTV disclosure requests with the council, TfL and any private operator. Day three: confirm engineer inspection booking, lodge signal-data and ANPR requests where relevant, and track every reference number into the claim file.
The reason this matters is the retention window. CCTV that was on a 14-day buffer at the time of the collision is gone by day 15 unless a disclosure request was lodged. The cost of a missed window is usually a liability dispute that has to be argued on photographs alone, which is winnable but harder than it needed to be.
Take action
If you have just been in a non-fault collision, the fastest way to protect your claim is to open the file with us inside the first hour. We dispatch recovery, lodge the relevant CCTV requests inside the retention window, and notify the third-party insurer for you.
