I'll try to help.
If you ask your question. I'll see if I can answer it.
Let em take a look at that and I'll get back to you.
I'm afraid that the lawyer is correct.
A deed of variation is a change to the will and that is effective for Inheritance Tax purposes whether it increases it or decreases it so long as all those affected agree. The £100,000 which was re-directed from your father was not a gift from him. Take a look here and here for confirmation.
I hope this clarifies the matter but let me know if you have any further questions.
I'm just following up to find out if my answer helped or if you have any further questions.