I did this today, so I thought I'd do a write up for you all!

Tools you will need:
Flat head screw driver
19mm spanner / socket
Spanner or socket for your new aerial.

1) Remove the trim clips around the boot. There are only three, and pop out quite easily.



2) Using the 19mm spanner or socket, undo the old mast.



You may want to have a cloth ready to clean your roof up! The cable for the aerial is quite short, but give it a wiggle, and it will come out of the socket.

3) When the old mast is out, you will be left with a decent size hole:


Reverse the procedure to install your new unit!

nice mod! whats the new aerial like? i may be tempted to do this as the rubber around my mast is deteriorating......

would you mind telling me where you sourced the new aerial?

Best bet is to eBay shark fin aerial.
The one I got isn't great, but does look cool! Suppose thats what you get when you only spend a fiver!

Ve-ery nice mate! Fiver? Not bad!

I'm pretty sure Carbon Fibre ones pop up on the US eBay from time to time...

Is it connected to the cars aerial/ functional or just for show?

It connects up, just not as good as the stock one.