I'm sorry I don't seem to understand... If I want to use savings then I have to show I have £21,000 and not £18600.No, although you can meet the shortfall with savings you have held for six months.
Example, you earn £16,600 so are short by £2,000. £2,000 x 2.5 = £5,000, plus £16,000. You would need to hold £21,000. This money can be a gift, but must truly be a gift with no expectation of repayment.