Tax in the UK also works differently to Aus and the tax system is one of the most complex in the world... in saying that, there is no requirement to lodge a tax return unless you're earning any income in addition to your normal salary, which is a good thing... but also means no juicy tax refund at the end of the tax year like many of you will be used to back in Aus!
The tax year here runs from 6 April to 5 April... yep... makes no sense! For anyone interested in the reasons why the tax year is on such odd dates check out this link.
It's important that you get your National Insurance number sorted ASAP once you get here to avoid being put on an emergency tax code and being charged far too much tax... on that point... tax codes are what HMRC uses to ensure the appropriate amount of tax is deducted from your monthly pay. If you are put on an emergency tax code but then get your National Insurance number sorted, HMRC will adjust your tax code so that you pay the appropriate amount of tax over the rest of the year i.e. you'll pay less tax on your earnings for the rest of the year.
It's actually a pretty cool system, but not without flaws (as per every government system). Sometimes you will pay too much tax, HMRC will automatically work this out and pay it back to you in due course, or you can request it yourself.
As we said, you're not required to submit a tax return (self-assessment here in the UK) unless you're self-employed or earn income in addition to your salary/bonus including dividends over the dividend allowance (Google "dividend allowance UK" to find out what the current allowance is).
The UK has four tax bands - nil rate, basic rate, higher rate and additional rate. You're best off Googling "UK tax rates" to see what the current rates of tax and tax bands are because these change every year.
In addition to your tax, a portion of your income will also be subject to National Insurance contributions. This is the Medicare Levy equivalent, except the rate is a fair bit higher than Aus for a good chunk of your income. Check out the current National Insurance rates of tax here (most people will be Category A).
If you leave the UK partway through a tax year and have no intention of returning, you can claim back any excess tax you've paid, but you can't claim back any National Insurance as this effectively goes towards covering the cost of any medical services you may or may not have accessed while you were here.