I don't think that this is a wise strategy at all.
If your borrowings exceed the value of your assets, you should not increase your borrowings to buy more property. You are exposing yourself too much to further falls in the price of property.
If at all possible, you should continue to live in your current property and use your savings to pay off the negative equity.
You will have to buy a house the old fashioned way - i.e. pay off the negative equity and start saving for a deposit all over again.
Brendan