Correct - 5.1% is about the best that you can get for 5 years - though I would not tie much up for that length of time - interest rates MUST rise within 6 months ..... (please !!)

I would consider sticking the whole lot in NS&I ..... Especially if you are HRT payer.

If you've used up your cash ISA allowance and dabbled with NS&I index linked certificated (5 years but easily withdrawable) then I guess long-term fixes are the next relaible savings alternative.

e.g. 5 years with an advertised 5.1% AER and paying basic tax £1000 will be worth £1221.