Thanks for the replies - really helpful.
nt00deep, you summarised the situation exactly. I'd rather use the cash for Stamp Duty and house furnishings etc ....
Munsterdude, I deliberatley did not complicate the example with the mortgage outstanding on the current house.
With this now included, I assume the figures would work out something like this;
Current house: 400k - (30k outstanding) = 370k
Now, 500 - 370k = 130k to borrow
I can still get deposit back ?
As for equity release, do you mean top-up the existing mortgage with the amount equivalent to the deposit, and the payback the outstanding mortgage + equity release value when closing ?