Understanding exactly what you can save into cash ISAs and Stocks and shares ISAs each tax year has not always been easy, as you could use your full entitlement if saving into a stocks and shares version, but for the Cash ISA you could only invest half the amount.
The March 2014 budget announced that ISAs are being revamped into a simpler product, with equal limits for cash and stocks and shares, plus a substantially increased ISA allowance. If you've already got an ISA (or ISAs), the changes apply to existing accounts too.
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