Interest rates shouldn't necessarily be higher because you've started a new job, and you can get a great deal when applying for a mortgage with a new job without delaying your application for months.
It's wise to remember that low-interest rates don't necessarily mean the mortgage is low cost.
Before getting a mortgage with a new job UK you’ll also need to look at arrangement charges, valuation fees, cashback offers or other incentives, and exit penalties before comparing two mortgage products on a like-for-like basis.