I don't disagree that aggressive tax avoidance needs to be addressed and it goes without saying that tax evasion is wrong. Thankfully the latter is low. Most money is 'lost' through tax avoidance rather than outright evasion.
But there is a point here to consider which is that often just because HMRC decide an amount is due, it doesn't mean it is so. There's been lots of other threads on this and there is a big grey area because tax is a very complicated matter.
So it's not as simple as waving a wand and collecting another £100billion(ish) of tax.
Outgoings I mean regular expenditure. Defence, welfare, education etc etc. link In fact, I just looked again and the annual expenditure is about £691 billion (2010-2011)
Total tax income is actually £447 billion. HMRC (2010-2011)
So the deficit is actually £244 billion.
I cannot see how we can seriously tackle this deficit without cutting welfare given it makes up £152 billion of our annual expense.
It would be akin to me being up to my eyeballs in debt and refusing to cut anything from my budget other than cancelling Sky TV. It's not a rational solution and no-one sensible will take your attempt seriously.
The top 10% of UK earners pay 50% of the nations income tax. So even if you doubled what they pay, you raise an extra £76 billion which still doesn't come close. And given our top rate of tax is already 40%-45%, I don't see how you would be able to actually bring it in.
It's not economics or politics which is driving austerity, it's arithmetic.