Lineside "railway scrap" is generated in one of three ways.
1) Excess rail and sleepers that have been created by track renewals. Generally the root cause of this is the poor specification of the works. Sleepers come in wagons with 56 sleepers per layer, a total of 168 per wagon. Network Rail are completely incapable of understanding that track renewals lengths really need to be based in proportion so that there are NO spare sleepers. If a few spares are required then they can be carried in Bass wagons.
Once the wagon loading is disturbed, then unused layers need to be re-strapped - a loading job for which TRC staff are not certificated, and DBS loading inspectors will not deal with. Because they in effect cannot be re-secured they have to be off-loaded to the trackside and in theory recovered at a later stage. Of course this nevers happens because NR is always on a mission to "save" money and will not pay the costs of recovery.
A similar situation happens with rail where there is a reluctance to reduce the length of LWR from the normal length, thus the excess has to be cut, and at that stage there are no trains on site into which the rails can be loaded.
Lengths of LWR can also be seen where a job has been reduced in length or cancelled. This generally happens when the TOCs demand to run late trains thus preventing the full job being carried out. There is no "sensible" criteria against which running a late train is decided thus a train with only one or two people on can cost tens of £0,000s simply because the TOC insist on running the train when it would be cheaper to give everyone a taxi home, and indeed a free annual season ticket to those punters in some cases !
2) Some lengths of renewals rail are left as "maintenance spares" to replace defective rails. They can give the impression of being scrap, and at some point they will become scrap, but in the meantime they provide a local supply of short rail for dealing with rail defects.
3) Scrap is generated by the Maintainer when he carries out piecemeal renewals and replacements, however there is no money or time allowed for him to collect his rubbish, thus it gets left there. Tne recovery of scrap generated from maitenance is probably at the bottom of the Maintainer's interests in all honesty.