Expenses allowed IR35 Public Sector Contract

There is one main place of work stipulated in the contract and client understands travel costs will be deemed ordinary commuting.

Also has to travel to second location every week and stay overnight and although the end client won't pay these costs client wants to repay from his Ltd Co.(He has other work/sales outside IR35)

I understood all travel within IR 35 excluded but is this correct?

Can anyone point me in the right direction of the legislation which covers this.

Many thanks