Because the UK & Ireland aren't part of the Schengen Treaty (which facilitates travel among certain EU member states), I would assume his UK residence permit would not be enough, and he would require a visa.
However please double check this with the French consulate in London. Their details are:
21-23 Cromwell Rd
020 7073 1200
or visit their website: www.ambafrance-uk.org/-Consulate-general-London-