I just think the whole argument is ridiculous. Our GDP is of order one trillion, i.e a million million, so that 170 million is about 0.02% of our total wealth. It's not going to make, in the grand scheme of things, the blindest bit of difference to our lives to withdraw this money compared to, say, cancelling trident, dealing with tax avoidance or stopping general government wastage.
There are anyway far better ways to save money than by withdrawing this payment of aid. It may well not be targets well, that's a separate issue.