Whether your travel to a work location counts as claimable business mileage or a non-deductible commute depends on whether HMRC treats that location as a temporary workplace or a permanent one. Get the classification wrong and you could miss out on legitimate tax relief or face an unexpected bill if HMRC opens an enquiry.
The rules sit in ITEPA 2003, primarily sections 337 to 342, and are expanded in HMRC’s Employment Income Manual from EIM32000. Two tests determine whether a workplace qualifies as temporary: the 24-month rule and the 40% test. This guide explains both, shows how they interact, and covers the situations that catch out contractors, secondees, and site-based workers.
What Makes a Workplace Temporary or Permanent?
Under ITEPA 2003 s 339, a workplace is any location you must attend to carry out the duties of your employment. A temporary workplace is one you attend for a limited duration or for a temporary purpose. Travel between your home and a temporary workplace is business travel, and the miles qualify for tax relief at HMRC’s approved rate of 45p per mile (25p after 10,000 miles).
A permanent workplace, by contrast, is the place you regularly attend to perform your duties. Your daily journey from home to a permanent workplace is ordinary commuting, and HMRC will never allow a mileage deduction for it, regardless of how far you drive.
You can have more than one permanent workplace at the same time — for example, if you split your week between two offices on a long-term basis, both may be classified as permanent. The key distinction is not how many locations you visit, but how long and how often you attend each one.
The 24-Month Rule Explained
The 24-month rule is the primary gateway. A workplace is treated as temporary provided your period of continuous work there lasts, or is expected to last, no more than 24 months. The moment the expected duration crosses the 24-month threshold — even if you have not yet completed 24 months — the workplace becomes permanent and travel to it stops qualifying.
When the clock starts. The 24-month period begins from the date you first attend the location for the relevant engagement. It is not reset by short breaks such as holidays or gaps between project phases unless there is a genuine material change in circumstances.
Intention matters. HMRC applies an intention or expectation test. If you know from day one that an assignment will last 26 months, the workplace is permanent from the outset and no travel expenses are claimable. Conversely, if an assignment originally expected to last 18 months is later extended to 30 months, the workplace becomes permanent from the date the extension is agreed — not retrospectively.
Contract renewals. If a contract is renewed or extended beyond 24 months, the position changes from the renewal date. You must stop claiming travel expenses once the total expected duration exceeds 24 months.
The 40% Test and How It Interacts With the 24-Month Rule
The 24-month rule alone is not sufficient. Even if your engagement at a location is under 24 months, HMRC applies a second condition under ITEPA 2003 s 339(6): the workplace is only temporary if you spend, or expect to spend, less than 40% of your total working time there over the period of continuous work.
The two conditions work together as a combined test, sometimes called the 40/24 test:
- If your engagement is 24 months or less and you spend under 40% of your working time there → temporary workplace (mileage qualifies).
- If your engagement is over 24 months, regardless of the percentage → permanent workplace (mileage does not qualify).
- If your engagement is 24 months or less but you spend 40% or more of your time there → permanent workplace (mileage does not qualify).
Example — consultant on a 12-month placement. A management consultant is placed at a client site for a 12-month project. She works four days a week at the client’s office and one day from home. Her time at the client exceeds 40% (it is around 80%), and even though the contract is under 24 months, the client’s office is treated as a permanent workplace. Her travel from home does not qualify for mileage claims.
Example — auditor visiting multiple sites. An auditor spends two weeks per quarter at each of five client offices, with the rest of her time at her employer’s head office. Each client site receives well under 40% of her time. Every client-site visit is a temporary workplace, and travel to each one is business mileage.
Contractors, Secondees, and Site-Based Workers
The temporary workplace rules apply differently depending on your working arrangement. Here are the most common scenarios.
Inside-IR35 contractors. If your engagement falls inside IR35, you are treated as a deemed employee of the end client for tax purposes. You have the same temporary workplace rights as a regular employee — meaning the 24-month rule and 40% test both apply. You cannot claim mileage through your limited company, but you can claim Mileage Allowance Relief (MAR) on your personal tax return for qualifying temporary workplace journeys. For a detailed breakdown, see our guide to IR35 contractor mileage expenses.
Outside-IR35 contractors. When working outside IR35, your limited company can deduct travel costs as a business expense. The corporate deduction route gives more flexibility, but the critical point remains: if you know an engagement will exceed 24 months from the start, the workplace is permanent.
Secondees. An employee seconded to another office or organisation retains their original employment. If the secondment is under 24 months and the seconded location receives less than 40% of working time, travel to that site qualifies as business travel. The existing contract — including pension and seniority rights — typically continues, distinguishing a secondment from a new employment.
Site-based construction workers. HMRC addresses construction workers at EIM32132. Workers who move between sites on contracts of varying lengths can generally treat each site as a temporary workplace, provided the 24-month rule is met per site. However, the 80% rule overrides this: if you attend a site for more than 80% of the expected duration of your employment, that site is permanent even if you are there fewer than 24 months. See our guide on construction worker mileage expenses.
Impact on Mileage Claims and Record-Keeping
When a workplace qualifies as temporary, every journey from your home (or between workplaces) to that location is business mileage. At 45p per mile for the first 10,000 miles, a contractor driving 8,000 business miles to temporary workplaces generates a deduction of £3,600 — worth £720 at the basic rate or £1,440 at the higher rate.
The key to defending your claim in an HMRC enquiry is contemporaneous records. For each journey, you need:
- The date of travel
- Starting point and destination
- Business purpose of the visit
- Miles driven
- The name of the client, project, or site
You should also be able to demonstrate that each location met the temporary workplace criteria — typically by showing the expected duration and frequency of attendance when the engagement began.
Tripbook records every journey automatically using GPS and lets you tag each trip with a client or project name, creating a real-time mileage log far stronger than a spreadsheet reconstructed months later. If HMRC asks whether a client site was temporary, your Tripbook records show the pattern of visits without manual guesswork.
How to Claim the Relief
The route to claiming depends on your employment status:
- Employees not reimbursed at the full 45p rate can claim Mileage Allowance Relief using form P87 (for claims under £2,500) or through a Self Assessment tax return. For the step-by-step process, see our guide on claiming mileage on your HMRC Self Assessment.
- Self-employed sole traders deduct business mileage on their Self Assessment return using the simplified expenses flat rate.
- Limited company directors can be reimbursed by their company at 45p per mile tax-free, with the company deducting the cost against corporation tax.
In every case, accurate mileage records are essential. HMRC expects evidence of each journey if asked, and claims based on estimates are vulnerable to challenge.
In summary, the temporary workplace rules are the foundation of every mileage claim for travel from home:
- A workplace is temporary only if you attend it for under 24 months and spend less than 40% of your working time there.
- The intention or expectation at the start of the engagement determines the classification — not just the actual time served.
- Inside-IR35 contractors, secondees, and site-based workers all face specific nuances that can change the outcome.
- Travel to a permanent workplace is commuting and is never deductible.
- Keep contemporaneous records with Tripbook to demonstrate the temporary nature of each workplace if HMRC enquires.
Download Tripbook from the App Store to start logging your temporary workplace journeys automatically.
