T+E only has a BS standard, there is no EN or harmonised standard, so in Spain it is not allowable. Also T+E has a reduced CPC Spanisg regs state that CPC is same size as L and N.
Pre Shuko spanish plugs were inline Pins with a slight ofsett on the Earth, thus giving polarity, also pre 2002 alot of boards had a double pole diff as a main with 1 x Single pole 16A and 1x10A MCB the individula circuits and socket outlets were then fused individualy on the phase.
Spain uses the Din style Shuko plugs and sockets which unlike the French do not have the protruding earth connection and can therefore be plugged in either way. I assume this is why they specify Double pole in the regs to ensure total disconection of the circuit.