Broadly speaking there are two types of Mortgage advisers or brokers. Restricted advisers, sometimes called tied, and Independent whole of market advisers.
Restricted, or tied advisers, for example almost certainly your bank, only offer a restricted number of providers. Independent, whole of market advisers can search the entire market and may have access to products that aren’t available to the public. So by all means ask your bank what deal they can offer but be sure to compare it to the best deal that an Independent Whole of Market adviser can get you and pick the best one.