We say dissertation for UG and PGT, but thesis for PhD.
That has been true of everywhere I have worked (not least because sometime our undergraduate dissertations can be better than our PGT's).
Yes, this is the way that it's usually done in the UK... but the point that I was making is that in the US the term Thesis is for undergraduate (writing a senior thesis) and Master's... the term dissertation is only used for Ph.D.
So... if folks from the US want to apply to UK jobs they need to be aware of the difference. On my cv I write: Ph.D. dissertation/thesis title: Underwater Basketweaving in South Carolina
MA thesis/dissertation title: Getting to Grips with Basketweaving