Cashing in Premium Bonds - how long

I found this on the NS&I's official website. It is taken from the premium bonds T&C's part of the site.

Repayment of Bonds
27. Bonds will be repaid at purchase price on application in writing to NS&I. Payment will normally be made by direct credit to a bank (including the National Savings Bank) or building society account in your name. You will need to give details of such an account in your application for repayment. The Director intends to use the Bankers' Automated Clearing Service (BACS) for this purpose, but reserves the right to use a different means of electronic transfer.

28. The date a Bond is repaid will be taken to be the date on which, in the normal course, the payment would be credited to the nominated account following initiation of the electronic transfer by the Director. In the case of BACS, this is normally two banking days after the Director initiates the transfer.

29. Where the Director initiates an electronic transfer properly, neither he nor the Treasury will be liable for:

(a) any failure or delay of the receiving bank or building society in crediting the nominated account;
(b) any failure or delay in any part of the electronic transfer process which is beyond the Director's direct control;
including any failure which occurs because the specified account is incapable of receiving an electronic transfer.

30. Payment can be requested by crossed warrant (like a cheque). In such cases the date a Bond is repaid will be taken to be the date on the warrant.

According to the above, repayment is made by crediting a nominated bank account - unless the bondholder has requested repayment by crossed warrant. I know this sounds silly, but are you sure that the funds haven't been credited to your nominated account? If they haven't paid you yet, then I think you should contact them to find out what is going on. On their website, the telephone number 0845 964 5000 is listed for all queries.