You'll also have to pay preliminatry tax for 2010.
Unhelpful.
He may not have to. We don't know level of rental profits he's likely to have, or indeed if he has any.
If you have taxable rental profits (normally revenue income less day-to-day normal outgoings less some (not all) mortgage interest (but ignoring capital repayments)) for 2009, and if you're up-to-date with employment/sole-trader taxes, you will pay tax on the rental property by the latest Oct/Nov 2010 on 2009 rents/income.
Generally at the same time, you will make an advance payment of tax for the 2010 tax year (therefore two years of a tax payment). (This 'double-payment is due to you just starting - normally however, in years gone by it was unlikely that rental profits would generate profits in the first few years so this wasn't an issue in the good old days).
In 2011, you will make a futher advance payment of tax for 2011. You will also pay tax/receive a refund of tax for the rental property where the advance payment paid in 2010 is greater/lesser than the actual liability for the 2010 tax year.
Filing dates for income tax returns are normally Oct/Nov each year. Dates vary depending on whether you e-file or paper-file.
PM me if you would like firther details or have fiurther questions.