theoretically if someone on my wireless network asks for wwww.google.co.uk could i then send a signal to the router that would stop the web-page from being sent, then send the packets from my laptop to make it look like i have hacked google

You wouldn't do that with packet injection. Trying to change data inside of an existing TCP connection requires getting the packet sequence numbers right and in general is pretty difficult.

But you could easily reroute DNS requests for Google to point to your local machine, then host whatever sort of page you wanted.

Though this is not the sort of thing LQ deals with, and asking for specific details on topics like this is frowned upon by the administration. If you can make the case that there is a legitimate or educational reason you want to know about a specific hack or exploit then you can get a little leniency, but it doesn't sound like that is what you are interested in...

I wasn't asking how to do it
Just wondering if it was possible

That's exactly the sort of thing Bill Clinton was trying to accomplish with the NSA's Clipper chip.

http://w2.eff.org/Privacy/Key_escrow/Clipper/