B v B  EWHC 543 (Fam)
"This is an application by the Official Solicitor for an order that Mr B do pay the Official Solicitor’s costs, on an indemnity basis, of acting on behalf of Mr B as his guardian ad litem, until the Official Solicitor was discharged by order of 19th August 2009."
Thanks to Alex Ruck Keene (39 Essex Chambers) for providing the judgment.
Possible Bailii link (not there when checked last night, but might have appeared since)
In 'COP costs cases' category as it is the nearest relevant category.