Nationwide are offering 3 year annual interest bonds at interest rates between 3.5% for under £9,999 and 3.85% for amounts over £50,000

more information: 3 year Fixed Rate ISA (annual interest) - savings interest rates and account summary from Nationwide Building Society

Balance
£1 - £9,999 3.50
£10,000 - £24,999 3.55
£25,000 - £49,999 3.65
£50,000+ 3.85