I am not sure if i am correct but I will try anyway:-) The important fact is when the bonus is actually paid. In our case it is paid in July following the y/e.
1. £10,000 paid in July 2009 – taxable in 2009/10 2. £15,000 paid in July 2010 – taxable in 2010/11 3. £18,000 paid in July 2011 – taxable in 2011/12