Overseas employment

I have a client about to go abroad to work for at least one full tax year.  He will qualify for non-residency.  He has asked me about journeys by his wife and children.  I though I knew this, but according to the manuals it appears these are only tax deductible if he remains UK resident and the trip abroad is for more than 60 days.  Am I misreading this?  Are family trips only allowable if you remain within the UK tax system as UK resident?