Your accountant does your tax returns so they should be in order.
HMRC takes the paperwork and checks that the accountant has done the job right.
This doesn't cost anything extra unless the accountant has made a mistake so why do you need
insurance to cover extra costs ?
That's not quite the process. HMRC take the accounts and questions everything in there, correct or incorrect. That's why it's an investigation; they are trying to find fault. Your accountant answers multiple questions on every single aspect of your accounts, for which he charges (as it's in excess of the work he's agreed to do for you). The bill can easily run into thousands. So it might be worth considering insurance, at least.
However, each to their own.
Vin
Its only an investigation if HMRC suspect that you have been up to no good, what some of us will get is a random check which for
a sole trader wont come to much.
They might find that you owe a few quid owe nothing or find that you have paid too much, until the audit is finished the accountant
doesn't need to get involved as the results will be sent to you the tax payer.
If you get a large bill which you suspect is wrong then arrange for your accountant to sort it out for a price.
If that price is going to cost more than the bill then pay the bill, its not rocket science even though some accountants would
try and make you believe it was.
Again if the accountant has done his/her job right and you have been honest then there wont be loads of questions to answer
just make sure you keep all your paperwork from 6 years previous.