Hi Bob,
I've asked Roger to clarify this point, but it being a Sunday and Father's Day, he may not a chance today.
However, I can tell you in the meanwhile, that AOM is right if the travelling you are referring to is from home to the yard that employs you (like me travelling to a permanent office address) and it's in the yard you stay and work - you can't claim tax.
However, if you are having to travel to many different sites to do your work (which I imagine you are) then that travel can be counted as an expense.
Roger will tell us more later.