SIC code 42120 classifies businesses engaged in construction of railways and underground railways. There are 2,578 active companies registered under this code in the UK, forming a substantial sector within the national economy. It falls under Section F (Construction) of the UK SIC 2007 classification system, which is used by Companies House to categorise all registered businesses.
See the full industry analysis on the Construction of railways and underground railways industry page.
With a 66% survival rate, this sector shows strong business longevity. Only 13 of 3,893 companies registered under this code have dissolved, well below the UK average. The average company age of 6.6 years suggests a relatively young and dynamic sector, with many businesses having been established in recent years. Growth has been exceptional recently: 48% of all active companies were formed since 2020, marking this as one of the fastest-expanding classifications. The 2010s contributed another 48%, meaning the vast majority of businesses are relatively new. The leading locations for this sector are LONDON (527), SIDCUP (41), DONCASTER (39), which together account for 24% of active companies.
SIC code 42120 stands for "Construction of railways and underground railways" under the UK Standard Industrial Classification (SIC 2007) system. It belongs to Section F — Construction. Companies use this code when registering with Companies House to indicate their primary business activity. The code is required for annual confirmation statements and is used by HMRC, ONS, and other government bodies for statistical and regulatory purposes.
There are currently 2,578 active companies registered under SIC code 42120 in the UK, out of 3,893 total registrations. This gives a survival rate of 66%, meaning 34% of companies registered under this code have since dissolved. These figures are based on Companies House data and updated regularly.
The top locations for construction of railways and underground railways companies (SIC 42120) are: LONDON (527), SIDCUP (41), DONCASTER (39), ASHFORD (37), BIRMINGHAM (35). Geographic concentration can reflect local economic conditions, industry clusters, or proximity to key markets and supply chains.
The sector is growing: 48% of currently active SIC 42120 companies were formed since 2020, and 48% during the 2010s. This sustained formation rate indicates ongoing demand for construction of railways and underground railways services in the UK.
Companies classified under SIC 42120 have an average age of 6.6 years. This suggests a balanced sector with both established players and newer entrants. Notable companies include SYSTRA LIMITED, VOLKERRAIL LIMITED, COLAS RAIL LIMITED.
Related SIC codes within the same division include: 42990 (Construction of other civil engineering projects n.e.c.), 42110 (Construction of roads and motorways), 42220 (Construction of utility projects for electricity and telecommunications), 42910 (Construction of water projects). Companies may use multiple SIC codes if they operate across several of these related activities. When registering with Companies House, businesses should select the code that best represents their primary activity.
You can search for companies with SIC code 42120 (Construction of railways and underground railways) using UVAGATRON's company explorer, which allows filtering by SIC code, location, and company status. Alternatively, Companies House offers a basic search on their website. Our platform adds risk intelligence, director networks, and signals from 50+ government databases to each company record.
Search, filter, and analyse 2,578 companies classified under this SIC code with AI-powered risk intelligence.
Data sourced from Companies House, HM Land Registry, FCA Register, and 50+ government databases. SIC classification follows the UK Standard Industrial Classification of Economic Activities 2007 (SIC 2007). Last updated: 2026-04-17.