Private Investigation Terms Explained: A UK Glossary

Updated 5 October 2026 by Investigation Bureau

This glossary explains, in plain English, the terms that UK private investigators, tracing agents and solicitors use, from OSINT, TSCM and skip tracing to process serving, statements of truth and lawful basis. Each entry says what the term means in the UK and, where it matters, where the law draws the line.

Investigation borrows its vocabulary from the courts, the police and data protection law. These definitions are general information, not legal advice, and each entry links to a fuller page where we have one.

People tracing

Tracing agent: A specialist in finding a person's current address for a lawful purpose, such as a debt, court papers or an estate. See tracing agent or private investigator.
Enquiry agent: An older British name for a private investigator, still used by solicitors and insurers.
Skip tracing: The American term for tracing someone who has moved without leaving a forwarding address. The UK term is people tracing.
Gone away: A person who has left their last known address with no forwarding address, a phrase taken from returned post.
No trace, no fee: Terms on which the fee is charged only if the person is found. Check that "found" means a confirmed current address.
Probate genealogist: A researcher who identifies and finds the heirs to an estate, often for a share of the inheritance. See locating an heir abroad.

Surveillance

Covert surveillance: Observation carried out without the subject's knowledge and recorded in timed logs, photographs and video. In public places it is lawful for a legitimate, proportionate purpose. See covert surveillance.
Static and mobile surveillance: Static surveillance watches a fixed point, such as a home or workplace. Mobile surveillance follows the subject on foot or by vehicle.
Counter-surveillance: Work to establish whether a person is being watched or followed, and by whom.
TSCM (bug sweep): Technical surveillance countermeasures: a physical and electronic search of a room, vehicle or device for hidden microphones, cameras and trackers. See bug sweeping costs.
Vehicle tracker: A GPS device that reports a vehicle's position. Whether using one is lawful depends on who fits it, to which vehicle and on what documented basis. See GPS tracker laws.

Fraud and corporate

Due diligence: Checking the background, record and standing of a person or company before a deal, an investment or a partnership. See corporate investigations.
Executive due diligence: A deeper check on a senior hire or board appointee: career claims, directorships, litigation, insolvency and reputation. See executive due diligence.
Asset tracing: Establishing what a person or company owns and where it is held, usually before deciding whether to sue or how to enforce a judgment. See tracing hidden assets.
Payment diversion fraud: A fraud in which a criminal poses as a supplier, solicitor or colleague and has a genuine payment sent to a different account. Also called invoice or mandate fraud. See invoice fraud.
Romance fraud: A fraud in which the offender builds a false relationship, usually online, to obtain money. See romance scam money recovery.

Digital and online

OSINT: Open-source intelligence: research using information that is publicly and lawfully available, such as social media, company filings, court records and the press. See OSINT investigations.
Attribution: Establishing, with evidence, who is behind an account, a message, a website or a payment. See who is behind an anonymous account.
Digital forensics: Examining phones, computers and stored data in a way that preserves the original and can be explained in court. It needs the authority of whoever is entitled to the device. See cyber investigations.
Open-source versus intrusive methods: Open-source methods read what is already public. Intrusive methods get into private accounts, devices or communications, and without authority they are criminal offences.
Unauthorised access: Getting into a phone, computer or online account without authority, an offence under the Computer Misuse Act 1990.

Court and evidence

Process server: A person who delivers court documents by hand and proves the delivery in a certificate or statement of service. See process servers in the UK.
Address for service: The address at which a party can validly be served with court documents, normally an individual's usual or last known residence.
Alternative service: Service by a method the court permits when the usual ones have failed, such as email, text or social media.
Letter before action: The formal letter sent before court proceedings begin, setting out the claim and allowing time to reply. Also called a letter before claim.
Witness statement: A signed written account of what a witness saw, heard or did, used as their evidence in court proceedings.
Statement of truth: The signed declaration that the maker of a document believes its facts are true. A false one, made without honest belief, can be a contempt of court.
Exhibit: A document, photograph, recording or object referred to in a witness statement and produced with it.
Continuity of evidence: The record of who has held an item of evidence since it was collected, also called chain of custody.
Admissibility: Whether a court will allow evidence to be put before it. Material obtained unlawfully can be excluded. See is investigator evidence admissible in court.
Norwich Pharmacal order: A court order in England and Wales requiring a third party mixed up in wrongdoing, even innocently, to disclose information such as the wrongdoer's identity.

Data protection and the law

Lawful basis: The legal ground that UK GDPR requires before personal data is used, recorded for each case before work starts.
Legitimate interests: The lawful basis most often relied on in investigation: a genuine need, such as recovering a debt, that is not outweighed by the rights of the person concerned.
Data controller: The organisation that decides why and how personal data is used, and answers for it in law.
ICO registration: Most organisations that handle personal data must pay a fee to the Information Commissioner's Office and appear on its public register.
Subject access request: A person's right to ask an organisation for a copy of the personal data it holds about them, subject to limited exemptions.
Pretexting (blagging): Obtaining personal information by deception, for example by ringing a bank and posing as the account holder. It is unlawful because it takes personal data without the consent of the organisation holding it, an offence under section 170 of the Data Protection Act 2018.
Interception: Listening to or reading calls, messages or post in transit. Without lawful authority it is an offence under the Investigatory Powers Act 2016.
Harassment: A course of conduct that causes alarm or distress, unlawful under the Protection from Harassment Act 1997. No lawful trace is run so that someone can be harassed.

Frequently asked questions

What is OSINT?

OSINT stands for open-source intelligence. It is research drawn from information anyone may lawfully see, such as social media, Companies House, the Land Registry, court records and the press. It does not include getting into private accounts or messages, which is a criminal offence.

What is TSCM?

TSCM stands for technical surveillance countermeasures, better known as a bug sweep. A trained operator searches a room, vehicle or device for hidden microphones, cameras and trackers, and reports what was and was not found.

What is skip tracing called in the UK?

People tracing, or debtor tracing where money is owed. Skip tracing is the American term for finding someone who has moved without leaving an address. The work is the same: confirming a current address by lawful means, for a lawful purpose.

What is an enquiry agent?

Enquiry agent is an older British term for a private investigator. Solicitors, insurers and local authorities still use it for a person who traces people, makes enquiries and serves court papers. Neither title is licensed in the UK, so the name tells you less than the firm's registration and methods.

A term we have not covered, or a problem behind it? Put it to an investigator in plain English. The first conversation is free: start a confidential enquiry.

Related on Trace Bureau, our sister service: Address tracing terms, explained plainly · What is a tracing agent, and when do you need one? · What is an enquiry agent?

Sister service: Trace Bureau is our fixed-price address tracing service, for anyone who only needs a current UK address for a lawful purpose. Charged only when we find them. Investigation Bureau is a Bureau Nine company.