If we are talking about resuming negotiations, then it is the UK who is refusing, since it won't negotiate under previous terms, i.e. it won't sit at the table one on one without the presence of the FI Government (or something along those lines; I'm not sure about the exact official British invitation). 
If you ignore those negotiations of the decades before the War, then it falls to a matter of perspective (point of view): 
 the UK refuses to negotiate without the presence of the FI Government (or refuses to negotiate and redirects negotiations to the FI Government; again I'm not sure); or
 Argentina refuses to negotiate with UK if the FI Government is involved in any way, or refuses to negotiate with the FI Government as the sole negotiation partner.

In this last case, who is "refusing" to negotiate is a matter of where the editor is standing.  (t)