The government made changes to the annual ISA allowance so that it would increase annually inline with inflation, beginning from the 2011/2012 tax year. This means you can save even more in your stocks and shares ISA and cash ISA, protecting more of your savings from capital gains and income tax.
If you do not invest the maximum allowance for 2012/13 ISAs before the end of the tax year (5th April 2013), you will lose that allowance forever. Additionally, if you withdraw money from your ISAs but have already paid in the maximum allowance for that year, you cannot replace the funds which you have taken out.