From the blog "IG Product Updates"
Turning on FX swap bid/offer
When trading currency pairs, if a position is held through 10pm GMT, it will incur an overnight funding charge. This charge is based on the interest rate differential between the two currencies in the pair, where you receive interest in the currency you buy and pay interest on the currency you sell. Swap rates also apply to cryptocurrencies and spot gold, silver, platinum or palladium.
Based on client feedback we have now added these overnight funding charg