She had been due to start as sales director of mortgages at Masthaven, after resigning from Castle Trust in April.
Instead Upton will move to Hampshire Trust to “work closely” with Matthew Wyles, the lender’s recently appointed chief executive, as the bank pushes into specialist lending.
The pair had worked together at Castle Trust.
Matthew Wyles said: “I’ve worked with Alex since 2013 and she is one of the most talented and hardworking executives in the mortgage market.
“Specialist lending is hugely important focus for us and Alex will play a crucial role in our success.
“I’m chuffed to bits.”
Upton added: “Hampshire Trust Bank is crystal clear about what it wants to achieve in specialist lending and its strategy for success.
“I am very excited to be joining the bank’s management team as we turn the vision into reality.”