Fitzy Tax really is the answer. I've already given one answer (pension contributions). I could give more, including the self-employed who pay themselves dividends instead of income, which avoids National Insurance. As I'm sure you know, NI is now 12% and is just another form of tax - a regressive one. They can also lower their tax by paying corporate tax rather than personal income tax and/or pay pension contributions (with a top of 40% from the government) in lieu of income. It's all perfectly legal, so could be stopped, and costs the country billions. That's before those who park their money offshore, but earn it in the UK, are taxed.
Council tax is another regressive tax, because the poorest generally pay a higher percentage of their income than the wealthiest. People in some of the richest areas, such as Westminster, hardly pay anything, while people in some of the poorest areas pay more for a property worth a fraction of a London property's value.
Tax collected from those who can afford it would make a huge difference.
I could go on, but I'm tired.