Unused inheritance tax question

WLJ60

I am about to start completing the online probate application and need to verify my understanding of unused IHT allowance. My father passed four years ago and left his entire estate to my mother, who has recently passed away.
My mother's home  was sold to cover care costs etc and her current assets are all in banks , building societies etc and are marginally over the 325,000 threshold. As my father left everything to my mother I understand she is eligible to his 325,000 allowance which more than covers her current assets. 
If this is correct do I only report the estate value when applying for probate or is there a separate form for HMRC.

I have spent quite a while reading various forum threads and Gov.uk guidance but clarification will be appreciated although Martin's video suggests I am correct, hopefully.

Keep_pedalling

You can claim the transferable NRB on the probate application and you have nothing to submit to HMRC. 

WLJ60

Thank you very much for this, most appreciated. Enjoy your cycling