Sir, – In your report “Phone company under fire over unreliable lines” a BT spokesman made incorrect claims about aluminium cables.

Besides having done the odd cable joint myself as an apprentice, I eventually served on the board of what was then the local face of BT, a Telephone Area (Reading) in the 1980s and we had already encountered high levels of maintenance problems on the then relatively new aluminium cables.

Aluminium is prone to corrode especially in contact with another metal like copper and that corrosion can actually turn a joint into a diode which mean current flows one way but not the other, In lesser form it increases resistance and introduces noise.

Aluminium is also brittle and prone to cracks when physically moved, say by a technician working on the cable or its neighbour, and these reduce conductivity and increase noise.

For broadband, any noise reduces speed dramatically, and it is nearly useless for another reason, as 1km of good quality aluminium has the same resistance as 1.5 km of copper, effectively moving the customer further electrically from the exchange.

If the spokesman has any doubts he should visit Adastral Park, the BT Research Centre at Martlesham Heath. Many employees lived on the estate nearby and it was wired using the then latest aluminium cable which later gave them rubbish broadband in sight of their employer’s most high-tech establishment.

JOHN LOADER West Witton, Leyburn.