For ordinary commuting even on a sub-24 month contract you cannot claim your travel costs, whatever your umbrella tells you. Here is HMRC's guidance.
www.hmrc.gov.uk/helpsheets/490.pdf
Fixed term appointments
3.18 A period of attendance at a place is not regarded as of limited duration or for a temporary purpose if it is all or almost all of the period for which the employee is likely to hold, or continue to hold, the employment.
Example
Everton is taken on for a fixed term employment of 18 months to work at a particular site. No relief is available for the cost of travel to and from the site during that period.