Hi, Craig. I wasn't aware such a thing as the Foriegn Enlistment Act 1870 existed. Thinking about it though, it makes sense that such legislation would exist. Any British government would be very unhappy to have a foreign power controlling the Iberian Peninsular. That's why they fought there in 1808-14. Spain in hostile hands means Britain's sea routes to India, Asia, and the Pacific are threatened. That's why they helped the Nationalists covertly. Franco's faction just wanted to win and control Spain, and rebuild it. One of their main fears would be the Republicans winning, and Stalin installing a puppet governmemt. Their next worst fear would be Franco dying, and the Nazis installing a puppet ruler. So they wouldn't openly support the Republicans. Ditto for the Nationalists, who were backed by Mussolini, and Hitler. The Neutrality Patrol didn't come into effect immediately however. A Labour government would be under a lot of pressure from it's left wing to aid the Republicans. They might conceivably have sent a pre-production Hurricane with blue prints to Spain before the arms embargo kicked in. They could also have sent some Gauntlets, or Gladiators. At any time after that, they could have sent something potentially as valuable. Intelligence information. For centuries, they'd had the best intelligence service in the world. Next, they could have manipulated their part of the 'Neutrality Patrol' to aid the Republicans. Ships could be allowed through. Lastly, they could have opened a line of credit for the Republicans. So, they'd have had more planes, men, and money. If the intelligence information had led to them winning a campaign, the war might have lasted longer. Maybe you could have them win the Vizcaya campaign, via an intelligence coup; or the one where they first used the International Brigades and T26s in large numbers. Then take it from there. So, even with restricted help, there is room to manouvre.
Even so, I'm not sure any of these measures would have allowed the Republicans to prevail. Given the factionalisim, disorganisation, and conflict on the Republican side, I think it would have been impossible for them to win. True, the Nationalists had factions. However, they were not as divided.
cheers
David Prosser