You certainly can - in the Catholic areas - and the only Catholic area in Britain is Gaelic speaking. But in the Presbyterian areas, especially the more fundamental varieties found in the islands, that would be inappropriate. (I don't understand the theological reasoning.) Note that despite enormous theological differences, and some different vocabulary such as for 'Sunday', Gaelic is not related to any sectarian divide in any way. In fact the reverse. Despite the opposing theology, the Gaelic areas were united in favour of Gaelic as it was the people in the middle, the Church of Scotland and the Episcopalian Church that supported the English who were trying to get rid of Gaelic.