They are allowed to carry 2 according to one engineer I had
This is based on my personal experience and was the subject of a complaint letter I wrote so maybe things have changed.
Engineer arrived at 9am to fix a known faulty box (I knew it had a HDMI problem as the engineer told me when he installed it but at that time I did not have an HDTV so no problem and in that case it was that box or book another day off for a new box!) Faulty box (as expected) but could not change it as he had used his alloted 2 already on the same problems already and would need to come back on a different with a new box
The long and the short was a lot of angry conversation with customer services managers and engineers and the box was eventually replaced ( twice as the first replacement packed up after an hour!)
