Oilseal the reason for the remote antenna or the re radiating antenna is if you car has a heat reflective windscreen this can block the GPS getting to the receiver. If you have a look at
http://www.totalpda.co.uk/product4481_0.aspx
Most recent Renaults like your Laguna do come with the heat reflective windscreen, if you look closely at the glass you can see thin wires, if you can see this it is definitely heat reflective.