What an Investment

Whilst having a clear out and rummage a couple of weeks ago, I unearthed this collection of Premium Bonds (The £1 one was bought for me by my Dad just after they were first issued).
Ever the optimist I sent the numbers to the Premium Bond people for checking.  Their reply was not what I wanted. "I am sorry you currently have no outstanding prizes".
They have been lurking within E.R.N.I.E for between 47 and 52 years with zero return - what an investment.  
I suspect they may be worth more as early examples of Premium Bond Certificates for collectors (if such people exist).