Should I wait for HMRC decision before naturalisation?

[Mochila]

I'm a US citizen, UK resident on ILR based on 5 years on a Tier 2 visa. Same job all along, tax paid via PAYE. I've been eligible to apply for naturalisation in the UK since Summer 2013, but have delayed the application pending a decision from HMRC. The HMRC decision relates to 4 years of taxes on interest and dividend income earned in the US. I'd only recently become aware that as a UK resident I needed to pay tax on this. My disclosure of tax owed was voluntary and unprompted, HMRC never asked me to pay anything. I've paid what I owe and have a letter from HMRC stating that my estimate of amount owed was correct. It's still possible, though unlikely, that HMRC will charge a penalty.

My US passport has expired. I don't want to renew this precious document until I apply for citizenship (using the Nationality Checking Service). Waiting for a final HMRC decision is a strain as I really want to get that US passport renewed, and I wonder if I am worrying over nothing.

Even considering that by making a voluntary disclosure to HMRC I was opening myself up to a tax investigation which has not technically concluded, can I now submit my citizenship application with confidence that I have met the "Good Character" requirement with respect to this tax issue? Might a red flag appear when the Home Office makes their investigation in to my tax affairs? I have settled all of my HMRC obligations aside from this one thing.

Thank you