I have finally settled on placing the new greenhouse towards the end of the mixed border quite near the large wooden greenhouse (putting it here means I can align it north south which is preferable to east west). However before reaching this decision I weighed up a large number of possible sites, all of which are illustrated below – apologies in advance for the weeds!
On the bottom patio
On the upper patio
In the top “Temporary Plants” border which abuts, none too happily, the wild garden