Karabiner custom bindings for UK keyboard; replace ~/Library/Application Support/Karabiner/private.xml

private.xml

<?xml version="1.0"?>
<root>
	<item>
		<name>Swap the GB pound symbol and sharp symbol</name>
		<appendix>Change Shift+3 to #</appendix>
		<appendix>Change Option+3 to £</appendix>
		<identifier>private.swap_pound_and_sharp</identifier>
		<autogen>__KeyToKey__ KeyCode::KEY_3, VK_OPTION, KeyCode::KEY_3, VK_SHIFT</autogen>
		<autogen>__KeyToKey__ KeyCode::KEY_3, VK_SHIFT, KeyCode::KEY_3, VK_OPTION</autogen>
	</item>
</root>