On Wed, 5 Oct 2005 00:37:41 +0100, "Epetruk"
wrote:

Let's say I have a paper travelcard that lets me travel from zones 2 to 6
and Watford Junction.

Let's also say I need to travel from Euston to Watford Junction.

If I buy an Oyster prepay card and I touch in when going through Euston but
don't touch out (because when I get to WJ I use my paper travelcard), what
will be the repercussions?

I'm not sure, specifically. But doing this would not be a Good Idea.
You'll get charged too much.