Grant of Probate time frame

HMRC don’t grant probate, the Probate Registry does.

Now you mention it, it's not clear to us whether the delay is with them or HMRC...it's all so opaque.
Could the solicitor be doing more?

How would any of us know?! Ask him/her exactly what is delaying matters. But I do know there have been backlogs at the PR due to covid. The size of the other estate is irrelevant - it might have been much more straightforward than your mother’s, which you say ‘isn’t particularly straightforward’. A more complicated estate would go to a more senior person at the PR. Simple estates are dealt with more quickly for obvious reasons.

Have you and your solicitor calculated the amount of tax due? If so and you are confident that your numbers are correct you should be able to go ahead and apply for probate.

You enter HMRC as a creditor in the statement of assets and liabilities to arrive at the net estate.

You can do this so long as you and your brother agree to this and agree between yourselves that you and he will settle any extra tax liability that you hadn't accounted for out of your inheritance.

Solicitors may be reluctant to proceed in this way where there are multiple beneficiaries. If further tax liability becomes due after the estate has been distributed, who pays? But if you and your brother agree you may be able to go ahead. You could ask for some money to be retained in a holding account as a contingency against a tax assessment in excess of what you have calculated.

This is what I did with my late husband's estate when we could not get HMRC to agree or disagree with final business accounts and tax calculations as submitted.

@Silverbridge, thank you for this - useful suggestion.

My mother died in September 2019, probate was granted by the probate office about 8 months later, our solicitor prepared and submitted the paperwork with our input. I’m surprised you mentioned inheritance tax, that has to be paid within 6 months of the death, or incur extra costs, we paid it on time. Monies from the estate were dispersed mostly in July 2020. Your solicitor should be keeping you informed, I have friends where probate has not been granted yet after 5 years due to family disagreements.

When Mil died 8 years ago I filled out the probate forms being the Executor. No inheritance tax however she owed money to HMRC and that had to be paid before probate was granted took around 5 months. HRMC forms were a challenge!

My godmother died several months ago. I have just heard from her solicitor that probate has been granted and he has got all the expenses sorted out. Just waiting to get an estimate for her headstone before he gives us a final figure, Apparently Covid has meant quite a run on headstones!

My mother died last year. Not complicated Probate, just her Flat and money. We did it ourselves -
Forms went in, pinged back they had arrived, and to our surprise granted within 15 mins.
Unbelievable! Just needed copies of Death certificate/Copy of Will in return post.