Nationwide Building Society has launched a table-topping cash ISA – but to get the headline rate, you can only access your money once a year.

The Single Access cash ISA pays 1.3% AER variable – the highest easy-access rate we've seen since December. The account is available to all and can be opened online or in branch with as little as £1.

The building society's also launched a new Single Access 'Loyalty' ISA offering a higher 1.4% AER variable, but it's only available to existing customers who've been with Nationwide for a year or more and have one of its current accounts, savings accounts or mortgages.

Both accounts accept transfers in from other ISA providers and pay interest annually.

However, there's one catch. You can only earn these rates if you make no more than one withdrawal per 'account year' – so in the 12 months after you open the account. If you make more than a single withdrawal you'll earn just 0.5%.

For a full rundown of how cash ISAs work and our current top pick, see our Top Cash ISAs 2017/18 guide.

What is a cash ISA?

An Individual Savings Account (ISA) is a tax-free way to save. Everyone in the UK has an annual ISA allowance – currently £20,000, and with the current tax year ending on 5 April 2018, anyone who wishes to make use of it only has a short time to do so. If you don't use it, you lose it.

But since April 2016, every basic-rate taxpayer can earn £1,000 interest a year without paying tax, while higher-rate payers can earn £500 – dimming the advantage of ISAs. For more, see our guide on the personal savings allowance.

How do the new Nationwide ISAs compare?

Cash ISA rates have lingered behind savings rates in recent times, yet these new Nationwide offerings buck the trend.

The 1.3% and 1.4% AER offered by these accounts easily beats the next-best rate from Virgin Money, Paragon and the AA, all of which pay 1.16% AER variable (the AA's rate includes a fixed 0.96% bonus for a year; this is basically a minimum rate guarantee, so be prepared to transfer to a better paying ISA when it ends). These accounts all offer unlimited withdrawals though.

However, if you aren't specifically looking for a cash ISA to stash your savings in, the highest easy-access savings rate is from ICICI Bank UK at 1.3% AER variable (including a 0.7% fixed bonus until 31 January 2018), followed by Tesco Bank at 1.26% AER variable (including a 0.71% fixed bonus for a year). Again, both allow unlimited penalty-free withdrawals. For full details and more options, see our Top Savings guide.