Thank you for all the constructive comments, so glad I'm posting in the DIY section and not passing myself off as a professional installer.
Maybe it's because I'm posting in the DIY section that very few of you bothered to read the original post and instead try to show just how much more you know about alarms than someone posting in this section. Does it make you feel superior?
The simple system was installed, complete & working. What's more, every function it was capable of, was easy for the householder to operate, not confusing and didn't need a security installer to explain to him every few hours. Thousands and thousands G4 panels have been installed and the simple (not new) technology employed is tried & tested and when an intrusion occurs they make the bell sound. They are easy to install and easy to understand, Is there something wrong with that for a DIY'er?
The expansion into wireless, after the installation, was due to the householder not accepting any visible cables and there being no access through the 2 extensions added to the property since the previous non functioning system was installed. These new areas where never going to be included within the system originally so adapting the final available zone to wireless was the only available option that would save the newly installed panel. £44 for the UR2, so all you experts can tell me how much cheaper than that a new combined wired & wireless panel would be.
As simlec says, faults within the wireless zones will trigger a tamper within the wired panel, clearly shown on the LCD keypad and exactly the same as if there was a tamper on the hardwired system. Could a householder diagnose & rectify that at 2am?
The UR2 also displays the event history for alarm (inputs), tamper (inputs or UR2), low battery (inputs), supervision (inputs), disarm (UR2) & arm (UR2). Not easy for the householder to get the history but better than not having coverage in the whole property. In any case if he has a tamper alert he won't be working out what's caused it, he'll be calling me.
Once again thank you to simlec for your guidance.