The Undergraduate Linguistics Association of Britain (ULAB)'s annual conference is the only one in the UK specifically for undergrads - any work completed while the presenter was an undergraduate within the last five years, in any area of linguistics, is very welcome. This year, the conference is from the 7th-9th April at the University of Cambridge.
Please encourage your undergrad students to submit here! It should be a friendly, informal conference to give students practice in presenting their work.
https://goo.gl/forms/j2PDBnnYhpNg90s63
The deadline for submitting an abstract for a presentation or poster is the 28th February; registration and payment will open later this month.