This has been bugging me for a while,

Just before christmas BT dug up the pavement along my street and laid some thick cables and duct along side the current ones and ran a new extra cable up each of the 4 telegraph poles on my street and added some new small boxes at the top of the poles. As far as I'm aware it wasn't to replace the current cables as the old cables still run up the pole and connect to the main connection box and I never had any loss in service while this was done.

What would be the reason for adding extra cabling like this to a residential street that is all houses and no businesses?

And I know that the underground cables enter the street at one end only as it's a dead end at the other.

When were the houses built?

Early 1920s

Then I suspect they are replacing the cables due to deterioration and soon they will swap over as planned upgrade of the network

I see.

theres probably a shortage of line plant (tel lines) so they have added more lines to the disribution points .on each pole.if they where upgrading the line exrta dps would not be fitted to the poles the whole lot would be changed .