HMRC allow travel costs to work for a period of 24 months for any one contract (or up to the point where you know the contract will exceed 2 years, whichever comes first).

After the 2 years, travel can be claimed for meetings and work at a place that is not your usual place of work. So for example if you have to go to a different location for meetings or training.

If you change locations, the clock is reset and you can start to claim travel again in accordance with the 24 month rule.