On the saloon the radio aerial is integrated into the heated rear screen. On the estate it's not. The aerial just forward of the boot lid also functions as a radio aerial on the estate but, for some reason, not on the saloon.
On the saloon the radio aerial in the rear screen is pretty pants at the best of times and is desensitised by the rear screen being on. If there's a nick in one of the conductors on the rear window or the power connections to the rear screen are poor, noise will wipe out the radio signal completely due to arcing, when the screen is switched on.
On the estate you might still get interference from the rear screen if the arcing is bad enough.
The bee sting antenna on the saloon is for a mobile phone. You can reach the rear of its' mounting hole quite easily by removing the trim panel that runs along the rear of the headlining above the back seat. It wouldn't be that difficult to replace it with a decent FM antenna and connect it to the coaxial cable that runs to the head unit, which terminates at a preamp box under the parcel shelf trim.
Note that if you have a head unit with integrated satnav or mobile phone you will need to keep the GSM antenna / GPS receiver that is, I believe, integrated into the antenna. Presumably an antenna from a suitably equipped estate would be a good starting point but I've never tried it.
Kefvin