Transferring messages between gmail accounts

[hackneylad]

Hi, quick question from a newbie:

I currently have two gmail addresses. For a whole number of reasons I want to transfer all of the messages/conversations I have in the inbox of one address to the other one. Does anyone know of any way I can do this relatively simply?

I've tried selecting all the mesages, attaching a label to them all, etc. but there doesn't seem to be any option available to forward them all together to another address. Apart from going through all the messages one by one and forwarding them individually (which isn't really possible because there are 6,000+ of them!) is there anything I can do?

Many thanks for your help, Jack