Right, back to Renault -
They called me back saying that they didn't have anything to replace the standard aerial, and just suggested, like Arran said, that I should get another bit of help tape. Obviously I wasn't satisfied with this answer, so I told them that I would be sending them an invoice for the correct aerial when I found one. Surprisingly he said OK!
Unfortunately being busy over christmas I haven't really been able to do much research, I've seen that Vivid White had cut his down, but we're still not sure if the signal is good enough for this to be a suitable fix. I have told RUK about this solution.
I also thought about the windscreen mounted aerials, but soon dismissed this as it looks rubbish.
I'm also in the process of upgrading my head unit, so hopefully this will boost signal, but obviously this isn't a fix that everyone can do cheaply.
Currently waiting for a reply from RUK about the modification to the standard aerial, but told them that I didn't want to do it unless they would send me a replacement standard aerial incase it isn't good enough!