a Net interest income

2007  2006  2005 
£m  £m  £m 
Cash and balances with central banks  145  91  9 
Available for sale investments  2,580  2,811  2,272 
Loans and advances to banks  1,416  903  690 
Loans and advances to customers  19,559  16,290  12,944 
Other  1,608  1,710  1,317 
Interest income  25,308  21,805  17,232 
Deposits from banks  (2,720) (2,819) (2,056)
Customer accounts  (4,110) (3,076) (2,715)
Debt securities in issue  (6,651) (5,282) (3,268)
Subordinated liabilities  (878) (777) (605)
Other  (1,348) (708) (513)
Interest expense  (15,707) (12,662) (9,157)
Net interest income  9,601  9,143  8,075 

Interest income includes £113m (2006: £98m, 2005: £76m) accrued on impaired loans.

Other interest income principally includes interest income relating to reverse repurchase agreements. Similarly, other interest expense principally includes interest expense relating to repurchase agreements and hedging activity.

Included in net interest income is hedge ineffectiveness as detailed in Note .