It's a tough one.
You are obliged to tell the lender that the circumstances have changed and when you do , they will do a review and will probably not give you the mortgage unless your partner's income is sufficient on its own.
If you don't tell them but tell your solicitor, she may feel obliged to tell them.
It's possible that you may have a clause in the contract that it is subject to the lender giving you the mortgage. If you have that, then you would get the deposit back.
The process with appealing your dismissal will take a long time and will not be resolved before you have to pay for the house.