Its a fuse, probably for the control wiring. Its a live feed for the timeclock for the E7 heating. A fuse in any case is the answer. The other block is a henley termination box.
You could get them to change that for a single rate meter and take timeclock out as its not being used if DNO will do it. Last one I tried to get taken out was told they don't do it and will only do it when meter is due to be replaced.
Generally nowadays they leave as is and add the two readings together and charge the normal rate. Saves money sending someone out to replace the equipment.