The tax year ends in less than two months' time, but nearly half of us (44%) have yet to use our full individual savings account (ISA) allowance, according to a MoneySupermarket poll - and are therefore missing out on valuable tax-free returns.

You can invest up to £5,340 into a cash ISA tax-free this year, and the same amount into stocks and shares, or you can invest the full £10,680 allowance into stocks and shares alone. But if you don't use this year's allowance by April 5, then it will be lost forever.

Despite the tax advantages of ISAs, our poll found that the main reason people have yet to use their allowance is because they can't afford to save.

Kevin Mountford, head of banking at MoneySupermarket said: "If you cannot afford to save, then review all of your outgoings and try to free up some cash which can then be used for savings. Even if you cannot afford to use the entire ISA allowance for this tax year, it is still worth opening an ISA, especially if you have existing savings held in other accounts elsewhere."

The good news is that, although the Bank of England held interest rates at 0.5% again this Thursday, marking nearly three years at this level, the rates on the best ISA deals are higher than those available this time last year.

The average rate of the top five cash ISA rates is currently 3.03%, which is a 7% increase compared to this time last year when the average rate was 2.83%.

Here, we take a look at some of the most competitive accounts currently available to help you make the most of this year's allowance...

Top variable rate ISAs

If you want to ensure you can get access to your savings in the event of an emergency, then you are better off going for a variable rate easy access ISA than a fixed rate account which will not normally allow any withdrawals.

There are plenty of easy access ISAs available which pay interest at least six times higher than the current Bank of England base rate.

Nationwide's Online ISA, for example, which accepts transfers from existing ISAs, pays an impressive 3.10% annual interest, but this rate is only available to those with at least £25,000 or more to invest. Savers who pay in the minimum £1,000 permitted to open this account earn a lower rate of 2.75%.

For those who don't have such a large sum to invest, Cheshire Building Society, for example, has just launched Issue 1 of its Direct Cash ISA, which pays a generous 3.06% annual interest tax-free. This rate includes a bonus of 2.06% which is only payable until the end of September next year, so you may want to move your money once this disappears. The Cheshire account does not, however, accept transfers from existing ISAs.

Other competitive easy access ISAs include Newcastle Building Society's Bonus ISA, which pays 3.05% annual interest tax-free. This account, which includes a 0.95% bonus payable for the first 12 months and does accept transfers, can be opened with a minimum investment of £1. The AA's Internet Access ISA pays the same rate of interest, but requires a higher initial deposit of £500 and does not accept transfers. A bonus of 1.35% is included in the rate, which again is only payable for the first 12 months.

Alternatively, ING Direct's cash ISA pays 3.00% annual interest on a minimum investment of £1, and this rate is guaranteed for a year. This account does not accept transfers.

Best fixed rate ISAs

The highest ISA returns go to those who are prepared to leave their money untouched in a fixed rate account.

For those who only want to tie up their money for a year, Virgin is paying a competitive 3.00% on its fixed Rate Cash ISA which can be opened with £1, and accepts transfers from existing ISAs.

If you can lock up your money for a bit longer than this, then as well as introducing a new variable rate ISA this week, Cheshire Building Society has also launched a market-leading 18-month fixed rate ISA paying 3.50% tax-free. The account can be opened with a minimum investment of £1,000 and no withdrawals are permitted during the fixed rate term. You can, however, close the account early, but this will result in a loss of 180 days' interest. You cannot make transfers into this ISA.

Leeds Building Society also launched new fixed rate ISAs this week, although these pay lower rates of interest. The one, two and three-year ISAs pay 2.25%, 3.00% and 3.05% annual interest tax-free and can each be opened with £1. You can transfer existing ISAs into this account.

The very best rates go to savers who can afford to lock into a fixed rate for several years. Bear in mind, however, that while longer term fixed rate accounts might look competitive now, they might not look quite as appealing when interest rates start to rise.

Halifax offers some of the best longer term fixed ISA rates, paying 4.20% on its five-year ISA Saver Fixed account, and 4.10% on the four-year version of this account. These accounts can be opened with a minimum investment of £500, and accept transfers.

Don't forget to review previous ISAs

Plenty of ISAs accept transfers from existing ISAs, so make sure you regularly review any accounts you've opened in previous years to see how much interest they are earning.

Kevin Mountford said: "If you have savings in ISAs you have opened in previous years, then it is worthwhile checking the rates being paid, as it is likely that you will be on a low rate. Switching an existing ISA balance to a market leading deal which allows transfers in can help maximise your savings pot. However, make sure you follow the official ISA switching rules otherwise your savings will lose their tax-free status. "

That means you shouldn't withdraw the cash to pay it into a new account, otherwise your savings will lose their tax-free status. Instead, you must request a transfer form from your new provider who should then arrange the switch on your behalf. It will also usually send you a note which you can forward to your existing provider to let them know you are moving your money elsewhere.

Please note: Any rates or deals mentioned in this article were available at the time of writing. Click on a highlighted product and apply direct.