The bank couldn't care less how much you would pay for your deposit. All they care is your ability on return the loan that you apply for. However, the bank would not loan you more than 70% of their evaluation price. You have to come up with the rest of the 30% deposit by whatever means.
Do you have a back up plan should you not able to sell your present flat and come up with the money in time to pay for your deposit of your targeted flat?