Vouchers can be bought for any monetary amount you wish, if you already have an account, login, go to My Account, scroll down the page to the Gift Voucher section, select an amount and then go through the checkout process. Once successful, you will receive the voucher via email for you to print out.
If you don't have an account with us yet, create an account, You will only need to create the most basic of accounts with us in order to purchase them, complete the first four parts, ignore the bit about adding riders to your account. Once you have done this, you will be able to login to your account, click on My Account, scroll down the page to the Gift Vouchers section, choose the amount you wish to spend, make payment and then you will receive the voucher via email.
Below is a guide on how to do this