Accrued Income on Sage

Hi, newish to accruals. Could someone please help?

YE is July. At 31.07.09 we had (let's say) £50000 accrued income. When I took over in Oct, the revenue that made up the accrued income balance had subsequently been billed and the money had come in:

So

1. 31.07.09 Cr Sales 50000 Dr Accrued Income 50000

2. Aug09 Cr Sales 50000 Dr Sales Control Account 50000

3. When the money was received Cr Control account Dr Bank

That still leaves a balance of 50000 in the accrued income account which makes it look like we have more left to bill than we do. What is the journal entry to reverse this and at which date should this be done?

Thanks in advance.