@blueshoes
Would be interested to know how often professional executors use asset training companies and what would be the trigger to use them and size of estate.
It's a decision made on a case by case basis. No hard and fast rules. It's entirely at the discretion of the executor(s) based on what information and documentation is available. It also has to be a balance - it can be cheaper just to appoint the asset tracing firm rather than spending dozens or hundreds of hours ourselves contacting different organisations, sifting through bags/boxes of random paperwork, etc. As you say, very different whether the deceased had shambolic records or whether there is evidence/suspicion of deliberate tax evasion. Must say it's not really something I've seen done very often, so certainly not a "go to" instruction without a proper evaluation of what you're presented with. Also probably not required at all if you've seen nothing to suggest any wrongdoing or "lost" assets and you can easily get all the close family to sign a disclaimer saying they've had no "gifts". After all, it's not the executor's job to disbelieve the people who claim they've had no gifts - we're not doing HMRC's job of "policing" the probate and IHT returns, we're just preparing them according to the information presented to us, augmented by enquiries we make. If it turns out a close family member has received a gift, lied to us about it, and gets caught by HMRC, then that's their problem, not ours, as long as we had no suspicions and no evidence to suggest otherwise. Back to due diligence. Of course, if a close family member refused to sign such a disclaimer, then that puts the executor on alert and may trigger additional digging work and maybe, yes, an asset tracing firm if there was a genuine suspicion of missing assets and/or undeclared gifts.
From memory, I think the most common situation of asset tracing firms being used is where a close family member simply doesn't believe the estate is as small as it appears, i.e. they "know" that their mother had some shares or they knew they had an investment account or a life insurance policy, but there's been nothing found in the paperwork, no sign of it when looking through bank statements, etc., and the family member didn't know any details, so without contacting literally every company, bank, insurance firm, etc., there'd be no way of finding it.