Kaitebeau I wish I could be as confident as you about the current government chasing after tax evaders and closing the loopholes of tax avoiders. Certainly Labour weren't brilliant at it when they were in government, to an extent they didn't have to because the financial services sector was overheating and generating huge amounts of revenue , so the government receipts were healthy enough. So Labour didn't have to pluck up the courage to track down the tax avoiders and make them pay their fair share.
Corporate tax avoidance has become much worse since the last election. Businesses feeling the squeeze look to reduce their costs, that includes their tax bill. Once one company finds a way to dodge tax others will seek to copy it. You end up in a viscious circle of companies that want to pay their fair share of tax not doing so because they have to compete with the tax avoiders. This is one of the big problems in the Greek economy, where VAT collection is poor. If you collect VAT on your business activities you end up 20% more expensive than your rivals, so in Greece you have to dodge VAT to stay in business. Corporate tax avoidance is essentially corrupting, and what happened to Greece is happening here. For example, Amazon has annual sales in the UK of £3.3 billion but pay virtually no corporation tax. This is because in 2006 they set up an office in Luxembourg which "bought out" the UK company, and the UK profits are siphoned off to Luxembourg where they pay a much lower tax rate. Since 2006 this has cost the UK government around £250 million. They employ several thousand people in the UK and only 134 in Luxembourg, but claim to be a Luxembourg company. They have repeated this trick across Europe, so all their sales through Germany, France, Spain, Italy etc. avoid tax in those countries. Any wonder that the EU economies are struggling when this is allowed? Since then many companies have followed suit - Ebay (and their subsidiary Paypal), Google, Boots (who were based in Nottingham for 150 years, but now claim they are based in Switzerland for tax purposes).
The government is aware of this tax avoidance but seems powerless to stop it. They often say that if they raise taxes on wealthy individuals then those individuals will just move abroad. But Amazon, Boots, et al. are not going to stop trading in the UK if they have to take a slice of their healthy profits and pay it as corporation tax. And the tax avoidance is unfair competition, because the local pharmacist or local bookshop can't choose to be based in a tax haven for accounting purposes, so it is harming UK based business.
Much of this could be tackled - the European tax havens could be tackled by co-ordinated EU legislation, and many other tax havens (Cayman Islands, Isle of Man, Channel Islands, etc.) are Crown Dependencies, so the British Government has massive influence here. That they choose not to act is either (1) they are afraid of the power of those with great wealth salted away in these offshore tax havens or (2) they are supportive of them. I suspect when Labour were in power it was (1), with the Conservatives it is (2). I say this because over 50% of Conservative party funding comes from individuals or institutions based in the City. So when they make policy decisions, whose interests are they working for?