Well the engineer duly arrived and after four hours of his hard work I'm pleased to report that I now have working broadband.
I don't really know what the problem was but obviously not something straightforward and not related to anything inside the property.
I think it may have related to some underground cabling mid-way between the cabinet and the property not being connected properly and a temporary socket installed in another cabinet but not removed giving the appearance of a working line with no faults but this may not be correct.
Anyway thanks for all your comments and advice.
