Mbna upgrade vouchers

Apologies if this has been asked before, but tried search for the answer.
I've had an upgrade voucher posted to my account, but theres nothing that says the T and c's anywhere.
How long do you typically have to use these? Is it 1 year or less or more?
Thanks for the help
I've had an upgrade voucher posted to my account, but theres nothing that says the T and c's anywhere.
How long do you typically have to use these? Is it 1 year or less or more?
Thanks for the help