UK MAIL labels to be integrated into Invoice/dispatch note

We currently use Royal Mail tracked & UKMail to send our products out though our website, however we would like to have the shipping label integrated to the invoice/dispatch note. As our warehouse are currently printing off the invoice and then a shipping label and then attaching them together and this is taking too much time. Also as these are loose these can fall off when the warehouse staff are using them to attached to the product boxes. We need this to happen very soon. We dont even mind paying for the change so everyone else can use it.