Just ordered a spare wheel from mytyres.co.uk, full size 175/65 R15 84H all-weather tyre on a steel rim. Price £78.60 delivered. Checked it will go in the space in the boot by jacking the car and actually trying an existing wheel (185/55 R16 83H) in there! And there is a threaded insert below the carpet to take a holding down bolt. We have a telescopic wheel-nut wrench so my wife can handle the untightening/tightening if necessary, as the supplied wrench is short. Hopefully won't have to use the spare but you never know. This gives peace of mind.
The jacking points were easy to identify and use with the supplied jack and taking the wheel off and on was easy, much better than using the supplied gunk which in any case won't work for anything but the simplest clean puncture.