If my wife and I opened joint bank or building society accounts with our children or grandchildren and put in the amount by which our assets exceed the inheritance tax threshold, would the money escape tax at 40%?
No. You actually have to part with the money and survive for seven years after making the gift for it to escape inheritance tax. Since you would still have access to the money in the joint accounts it would be regarded as a gift made “with reservation” and be reckoned part of your estate for inheritance tax purposes. See a solicitor specialising in financial planning for detailed advice.