The 24 month / 2 year rule is a time period set by HMRC which allows travel and subsistence expenses to be claimed whilst working at a ‘temporary’ workplace; such as a client’s site. After this 24 month period, the workplace will be classed as permanent and travel expenses can no longer be claimed. The rule also states that as soon as you have visibility of being at that temporary workplace for more than 2 years you must stop claiming travel related expenses straight away, i.e. you cannot claim continuously for 2 years.
The 24 months begin when you first start travelling to the client’s site and last until the end of the contract. If the contract is or is assumed to be less than 24 months, then travel expenses are allowable. However, as soon as you know that your contract will exceed 2 years (for example you complete an 18 month contract and then accept a further 12 month contract) you can no longer claim for your expenses.