The sorry state of interest rates for Cash Isas and savings accounts generally means you're by no means alone in trying to find a better rate for your tax-free nest egg.
A number of banks and building societies have cut the interest rates on variable-rate Isa products in the past three months.
I think the Clydesdale Bank Isa that you refer to is the 40 Day Notice Account. You are correct in that it pays 2% AER, however this is only for balances of £24,000-plus. If, for example, your balance is between £9,000 and £23,999, the rate is 1.5% AER.
Something else you should bear in mind is that this is a variable rate Isa, which means the bank could reduce the interest rate at any time – just as Nationwide Building Society has done with your existing one.
To secure a more rewarding cash Isa rate and one that's fixed means having to tie your cash up for a period of years.
For example, with the Post Office you can earn 1.95% AER for a term of two years. For a four-year product, the top rate is 2.2% from Nationwide Building Society and to earn 2.5% you'd need to lock your cash away for five years with Virgin Money.
The rate differences are quite small, however. On a £15,000 balance, an extra 1% tax free on the rate will see you earn an additional £150 in interest over a year, so whichever new Isa product you decide to plump for it's definitely worth moving your custom elsewhere.
With interest rates predicted to start moving upwards in the next 12 to 18 months, I'd be reluctant to lock into anything longer than two years.
Aside from putting your Isa money in cash accounts, you may wish to consider moving some of your tax-free balance into a stocks and shares Isa.
However, I would strongly recommend that you seek independent advice from a local financial adviser before going down this route. It is possible to get a better return with equity-based investments but it's by no means guaranteed or risk free.
Reply from Andrew Hagger, founder of personal finance website Moneycomms.co.uk