I should have been more specific, I mean long sections of rail in the open where there are large stretches of bullhead, I find it amazing that over 50 percent is bullhead as I rarely hear the "clickety clack" sound when using the met or picc.
People often make the mistake of equating Bullhead rail with jointed track. The Underground, however has been using long welded Bullhead rails for decades. HG Follenfant, in his 1975 book 'Reconstructing London's Underground' has a section on track and rails. In it he notes that the Underground established a rail welding plant at Lillie Bridge in 1938, and that until 1949 it was the only rail welding plant and in the U.K., thus any long welded rails installed anywhere in the U.K. prior to 1949 were welded at Lillie Bridge, and that it was not until 1960 that the mileage of welded rails on BR exceeded that on the Underground. The Underground's original approach was to weld rails into 300 foot lengths with machined rail ends. These lengths would then be jointed on site in the normal way, except that no expansion gaps would be provided. This would produce an effective continuous rail up to half a mile long. Expansion joints were provided at half mile intervals. At a later date on site rail welding would be used to joint the 300 foot rails. The Underground's motive for the early adoption of long welded rails was to reduce the number of rail joints in a given length of track. Rail joints are maintenance intensive, and when you can't access the track while trains are running (because it is in a tunnel) anything which reduces the time required for maintenance is a boon. The transition from Bullhead to flat bottom rail was a different issue. On BR the change was driven by the desire for higher train speeds ( flat bottom track is more stable than Bullhead) and for greater axle loads. The Underground needed neither of these things and so the transition was delayed until it was simply cheaper to install new flat bottom rail rather than Bullhead.
Another Q,(im pushing it I know :p), on the Baker Street SCC diagram, what do the outwards pointing transverse arrows near Euston Square represent mean?
-Edit- After some thinking (using the term loosely here), I guess they are Limits of Shunt. Is this correct?
They are not limits of shunt. They are site boundary markers. The area controlled by Baker Street SCC is divided into eight computer sites. Each has a pair of local site computers controlling the signalling in that area. The computers also handle all indications from the signalling system in their area and relay these back to the SCC. In the event that both computers on a single site fail then all control and indications are lost for that area, and the boundary markers help the signalmen identify the exact limits of the area affected. The boundary markers at Euston Square denote the boundary between the Baker Street site and the Farringdon site.
I've always assumed that buildings of that style were associated with traction current supplies. There are several such buildings dotted around the network. Referring to the yellow peril for Newbury Park I find that there was a traction switch house located more or less where the brick building you describe is located. I suspect that this must be what the building is. The traction switch house was provided in connection with the long gone car sidings and allowed them to be fed from either the inner rail or from a direct feed from Newbury Park substation. The switch house also contained the circuit breaker for the sidings, which was effective regardless of which supply was used. Presumably it was the presence of the circuit breaker which necessitated a full blown brick structure, rather than the more usual changeover switches in yellow boxes.