The spikey one is Datura (probably D.stramonium) or thorn apple. It's an annual.
The smooth leaved one has been reclassified as Brugmansia - shrubby & woodier, and perennial. There's more info here -
http://www.clisby.eclipse.co.uk/angels-trumpets.htm

Thanks Beattie, owe you a drink, won a fiver out of that one. X

LOL Don't know when I'll be visiting Kent to collect! :-)

They are very closely related. Rule of thumb for I.D.: Thorn Apple flowers stand up, at least at an angle, and the pod is round and spiny or bumpy. Angel's Trumpet flowers hang down, and the pod is smooth and cigar-shaped.