Countries over-achieving in their first period commitments can "bank" their unused allowances for use in the subsequent period.

Interest is paid net of basic rate tax and non-taxpayers and investors with unused allowances must reclaim tax.

Where pension contributions exceed the AA, unused allowance from up to the three previous years can be carried forward to offset against the excess contribution.

If you don't pay tax and your spouse or civil partner does you can still transfer your unused allowance to them.

They could accumulate unused excess allowances by running their cleanest plants, and then sell or trade the allowances to other operators in an open market.

CREATE a central fund into which all unused allowances from new developments can be fed, to be drawn upon as a way of reducing customer contributions on infill projects.

Since many purchases were made in earlier years, and unused allowances have accumulated, these groups own the right to emit 16,547 tons of sulfur dioxide in 2011.

To protect individuals who exceed the annual allowance due to one-off "spike" in accrual, the Government will allow individuals to offset this against unused allowance from previous years.

Polluters are even allowed to squirrel away unused allowances for future use or sale.

Emitters exceeding their quotas must buy carbon permits, while those within their limits can sell any unused allowances.