139 How you can save NATIONAL SAVINGS comprise the following channels of investment : National Savings Certificates. A Certificate costs 10s. and increases to 13s. in 10 years. The increase is free of income tax. You may hold 1,000 of the present issue of 10s. Certificates, in addition to permitted holdings of Certificates of previous issues. Defence Bonds. These Bonds earn interest at the rate of 21/2 per cent. per annum : they may be purchased in multiples of £5. You may hold up to £2,500 of Defence Bonds.