13 British nationals have received death sentences in foreign countries and 51 more are potentially facing the same sentence, according to evidence submitted to the High Court by the FCO.
Aidan O'Neill QC said it was suggested that FCO assistance would "open the floodgates" and create several difficulties.
However, he suggested that the amount being sought to meet the costs of an Indonesian lawyer for Lindsay Sandiford was not a substantial amount of money.
Martin Chamberlain, appearing for the FCO, said it would be difficult to limit a strategy of providing assistance to death sentence cases.
He said there would be pressure to extend the scheme it to other human rights cases where the "human dignity" of other British nationals came under threat.