Once the examination has been successfully completed, the application is published in the UK Trade Marks Journal. Following publication of an application, there is a two-month opposition period (extendable to three months), during which any third party may oppose registration of your mark on the basis of earlier rights.
To be successful in an opposition, another party would need to prove that they have an earlier right to a similar or identical mark in relation to similar or identical goods and services, leading to a likelihood of confusion.