You are right that you have to spend a full tax year (6 April to 5 April out of the UK to claim tax free earnings.
So if you got here on, for example, 13th April 2006, your tax year wouldn't start until 6 April 2007. Then you would have to stay in Qatar til 5 April 2008.
In short, you have to cover that full designated tax year.
It is very tricky, Serendipity. But here goes:
You are right that you have to spend a full tax year (6 April to 5 April out of the UK to claim tax free earnings.
So if you got here on, for example, 13th April 2006, your tax year wouldn't start until 6 April 2007. Then you would have to stay in Qatar til 5 April 2008.
In short, you have to cover that full designated tax year.