not worth the paper it's written on. most policies for example say the estate agent must confirm in writing that you've been gazumped or the seller has pulled out. which none of them will ofcourse provide.

It would make more sense with a mortgage as you have costs such as broker fees, appication fees, valuation fees, that is lost if the sale falls through. If your buying cash the same policy is covering a lot less, plus if your a cash buyer you can complete rather quickly so less time to get gazumped.