I worked for HM Customs & Excise which then merged with Inland Revenue to form HMRC for 27 years. I was made redundant in 2022 when my local office finally closed.
Instead of being situated in nearly every major city in the UK I think there are now approx 16 regional offices in the UK and I doubt many of them have the old drop in enquiry centres that we used to have.
There will be a massive skill shortage as for decades HMRC did not recruit tax specialists, in an office of 100s I was one of the youngest for most of my career, I'm now in my 50's.
The movement to contact centres did have heavy recruitment but all these civil servants were taught were call scrips, no in depth knowledge of the multitude of taxes that HMRC administer. Constant fire fighting and moving priorities on the back of whatever political pressures are the favourite of the day lead to demotivated staff who want to do their best but are constricted by 'call stats' and pressure from management to simply improve the 'call stats' rather than solving issues and providing actual customer service.
Also a massive issue is the devaluation of the role of a civil servant. Back in the day when I was a visiting vat officer I was paid a decent amount as an Officer. These days a 'compliance officer' as they're now known would be paid around £28,000. Those working on taking calls in a contact centre as assistant officers are paid minimal wage. Minimal wage! For a high pressured role where you gets dogs abuse from the public day in day out, pressure from your management, and have no say in how things can be improved, no ownership over your tasks etc. it's honestly a shit show.
To have a good effective tax system we need to invest in our Civil Servants, get the right people for the job, train and invest in them, pay them appropriately, encourage professional development. Then you get people who are proud of what they do and want to serve their public to the best of their ability.
I've not looked back, except with relief, since I was made redundant (with a huge payout, imagine the cost of that for the 10,000+ staff paid off on recent years due to the restructuring to regional centres, not to mention all the experience lost!)