Colin, try and go to a store and test your iphone on it, i have a DAB radio in the kitchen with iphone dock, but the phone radio signal interferes with the DAB radio and i get that horrible noise you get when two radios "collide" the only way round it is to put the phone into airplane mode..
To be honest, the one i bought was cheap as chips, so its probably not designed to work with an iphone, only ipod..
I have a Pure one in the house and one in my car, plus a Roberts one in the house and they are all fine. I do seem to remember reading that Sainsburys own brand ones, I think the brand is called Red, are superb value as they are ones made by proper radio makers but just rebranded and cost half the price of what you'd pay if it was not from Sainsburys.