By Isla Binnie MADRID (Reuters) – Power trading platforms are urging the Spanish government not to intervene alone in the system that sets the price of electricity, in its bid to bring down sky-high utility bills, according to a letter seen by Reuters. European countries are scrambling to agree on ways to manage surging gas and power prices, pushed higher by Russia’s invasion of Ukraine, which are eating away at people’s spending power across the bloc. Spain and Portugal received permission in March to take their own temporary measures to contain prices. The neighbours have been working on way…