In my opinion and experience, the best at HMRC are top flight. Smart, pragmatic, commercial, intelligent, creative. No different, in fact from the better private sector tax experts. The issue is that the average HMRC employee is, frankly, not on a par with the average private sector tax person.
Now, that doesn't matter as much as you might think, because the vast majority of taxpayers are small businesses who aren't interested, and don't have the resources, to get involved in tax planning. So the mismatch is smaller than it first appears.
It was an issue when average Inspectors came up against the cream of the private sector. However, HMRC and the Treasury have been smart on how they counter this.
First, they introduced the disclosure rules. They say that if someone in the private sector comes up with a cute tax planning scheme then by law they have to disclose details of how it works to HMRC within a very short time frame - think days rather than weeks. That means that HMRC can very quickly act to counter avoidance by changing the tax legislation.
Secondly, they have implemented a new policy of trust and transparency between HMRC and big business/high net worth individuals. Each taxpayer in the programme has been assigned a risk rating by HMRC, and believe me it's a rigerous process. A low risk rating means HMRC have reviewed your affairs, accept that you're compliant and will apply a light touch in dealing with you. A high risk rating means HMRC will pay you far more attention, and not in a good way. The carrot for tax payers is that where there are areas of genuine uncertainty over how the law should be applied (which crops up all the time, especially with complex companies which are generally defined as the largest 10,000) then HMRC will help them come to a fair and commercial agreement.
Thirdly, HMRC have spent a lot of time and effort identifying risk triggers across all taxpayers (not just big business/HNWI). They're focussing their efforts far better and getting results to prove it.
HMRC, like most of the 103 departments, are facing spending cuts of 25%. However, unlike the rest they're getting 10% back specifically to tackle avoidance and evasion. So their actual cut is only 15%. Clearly it will effect headcount.
HMRC thinks that it can cope with most of this through efficiency savings (e.g. increased automation, take effort away from the compliant majority and focus it on evaders/avoiders/those who want to be compliant but need more help). I think that there are undoubtedly efficiency savings to be made, but I'm sceptical that it there's enough slack in the system than it will absorb all of the pain.