My apologies - type of question one needs to get right!
I assumed by giving a gift up to the value of the IHT band on my death, the band has then been fully utilised. Therefore my wife could not claim it a second time on her death as there is no unused threshold to carry forward.
Instead, if tax is payable by making a gift via my will as above, I could direct that my wife makes a gift (by way of a letter of wishes) to my children of equivalent value of the IHT band after my death. Assuming she survives 7 years then no tax would be payable by her estate.
Just trying to keep everyone happy here.