Irrecoverable rent

“Softapp Ltd let out a warehouse surplus to its requirements on 1 October 2016, the monthly rent of £5,000 being payable in advance on the first of each calendar month. The rent due on 1 March 2017 was not received due to the business failure of the tenant. Half of the unpaid rent was received on 10 April 2017 and the rest is irrecoverable.”

The property business income has been calculated as follows:

£
Rental income receivable 30,000
Less irrecoverable rent £5,000 × 1/2 (2,500) >>> ?????
Property business income 27,500

I am confused. I know that property business income is assessed in the accruals basis.

I don’t understand how the irrecoverable rent is 2,500. Shouldn’t it be 5,000 since it wasn’t received in the current accounting period?