"The main tax avoidance mechanism involves a limited company and favours large companies, and the Government seems disinterested in tackling this."
With apologies for going off topic, but the statement above is factually incorrect.
The tax gap in the UK (that is, the difference between the amount of tax that should be collected and the amount that actually is collected) is around £40bn. That compares to total taxes collected of around £400bn - so about 10%.
Of the amount missing, somewhere between £5bn and £10bn is down to avoidance across all businesses and individuals. I certainly agree that the majority of the avoidance is due to high net worth individuals and companies (although not necessarily large companies - in my experience medium sized owner managed companies are far more likely to want to push the boundries).
Another £10bn or so is due to inaccuracies, where the error is accidental. Some of it is timing differences (so, for example, where a trader records VAT in Q1 of Y2 when it should have been paid in Q4 of Y1) that will unwind automatically. A lot more is where people simply fail to understand how the rules should be applied, particularly around one-off transactions.
Around £20bn is down to deliberate fraud or criminal activity. Evern HM Revenue & Customs acknowledge that this is almost exclusively the preserve of sole traders. It's the builder working cash in hand, the contractor falsifying receipts, the trader who fails to declare income, the moonlighters and payroll ghosts.
The problem for HMRC is that it's incredibly hard to catch the millions of people who commit this kind of low-level low-value fraud. It's even quite hard to spot unless we're willing to pay for thousands more investigators who can spend literally weeks watching soletraders at work.
By all means crack down on avoidance. In my view HMRC is actually doing a pretty good job of it. Tax schemes are being challenged more and more often, and are closed down far more quickly, and are taken to the courts for arbitration on a regular basis.
But we should also focus on the largest source of missing revenue - fraud.