The Britons did use numerous 'big' weapons, for their nobles and greatest warriors. They did not have the iron reserves available to Gauls or Iberians or Romans, because they did not, individually, control much land. They would sometimes make BIG weapons, like greatswords and big axes (which were essentially modified wood axes, but a heavy axehead is a heavy axehead). There are also some evidences of falcata-type swords, but those are fachoira, and probably brought over by Gaelic raiders, who, in their early periods, employed these weapons. The Britons were bigger on spears, slings, javelins, that manner of thing, lots of wooden weapons, including proto-maces that were essentially glorified clubs, wrapped with leather strips, or with bronze or sometimes iron fixtures in them. The Britons are going to be, I think, based largely on their actual historical strengths. That's mobility and raiding abilities, so units that can hide well in forests/tall grass/anywhere, will probably be a bit more prevalent with the Britons than other armies, more 'fast' units. I'm thinking greatswords and big axes for officers now, as while the evidences exist, they were quite rare. Unless units employing them were small, I don't think I could see them as being too realistic. But an officer accompanying his men with well-made, modified wood axe, or a big two-handed sword, that'd make sense. Two-handed swords were more popular with the Gaels, who imported a lot of iron, and had fair enough iron reserves at the time, and have many more examples of the large two-handed swords from the BCs, but they're clearly based on earlier British greatswords.