UK SIC 2007 · 43999
Other specialised construction activities n.e.c. (SIC code 43999)
Other specialised construction activities n.e.c. is UK SIC code 43999. It sits in division 43 (Specialised construction activities) of the SIC 2007 list. On the August 2026 Companies House register, 62,240 active UK companies list 43999 among their SIC codes. 47,320 of them list it first. That makes it the most used code in its division.
Division 43: Specialised construction activities
This is the trades division, and one of the biggest classifications on the UK register. Electricians use 43210. Plumbing and heating engineers use 43220. Roofers use 43910. Plasterers, painters, glaziers, floorers and scaffolders each have a code of their own. Two broad codes swell the numbers further. Code 43999 covers specialised activities not elsewhere classified. Code 43390 covers other building completion and finishing. Both soak up general trades and multi-skilled firms. Most companies here are small. Many are one tradesperson who went limited for contracting or tax reasons.
Who prospects SIC 43999 companies
Lots of firms sell to the trades, because their needs are predictable and repeat every year. They buy public liability insurance, accountancy for CIS refunds and company compliance, van leasing, tools and trade credit from merchants. Lead generation and website services aim at the poor-website filter. A tradesperson whose site fails basic checks loses local work to rivals who show up in search. New incorporations are the standout signal. They usually mark the jump from sole trader to limited company, when insurance, banking and bookkeeping all get chosen in a few weeks. Heating firms under 43220 also attract renewables sellers, especially heat pump distributors.
Lead generation for trades & construction →How to read SIC 43999
SIC 43999 is a five-digit code, and the digits are not arbitrary. The first two, 43, are the division, specialised construction activities. Add the third and you have group 439; the fourth narrows it to a class, and the fifth to the subclass, which is the level Companies House actually asks a company to pick. The whole division sits under section F, construction, the broadest tier there is. Reading a code left to right therefore goes from a whole sector down to one activity.
A company chooses its own codes when it incorporates and can change them on any confirmation statement. It may list up to four, and Companies House does not check whether they are right. That is why 43999 is worth reading as a claim the company made about itself rather than as a verified fact, and why the first-position and any-position counts above differ.
Measured on the August 2026 register, the busiest registered-office post towns for 43999 are London (8,289), Glasgow (828), Manchester (808), Birmingham (728) and Bristol (656). Those are registered-office locations, which is where the paperwork sits rather than necessarily where the work happens, so treat them as where to start looking rather than as a service area.
Using SIC 43999 as a filter
62,240 companies is 1.2 per cent of the 5,190,464 active companies on the UK register, and ranks 43999 most used of the 15 codes we track in division 43. That is the pool before any filter. Whether it is a big market for you depends on what you sell, but it is the number every other filter on this page cuts down from.
47,320 companies put 43999 first and a further 14,920, 24 per cent, list it in one of their other three SIC slots. That gap is the difference between a tight list and a broad one. First-code-only is the safer filter when you are writing to them; matching any position is worth it when you need the volume.
These companies are spread out. London is the largest single cluster at 13 per cent and the top five post towns together hold only 18 per cent, so the remaining 82 per cent sits across the rest of the country. A regional filter narrows this list without gutting it, which makes it a reasonable code to work territory by territory.
In practice the code on its own is rarely the whole filter. Pair 43999 with an incorporation date to catch companies in their first months, when they are still choosing suppliers, or with a filing deadline to reach them while the year end is on their mind. A worked example for this code: 43999, registered office in London, incorporated in the last ninety days, which turns a 62,240 company pool into a list you can write to in an afternoon. Add the poor-website filter if what you sell is a website, or a recent change of officer if you sell to whoever just took the job. Every company you pull carries the Companies House record, the director's name, a verified website and a verified email, and the ones we cannot complete are not charged.
Where SIC 43999 clusters in the UK
ACTIVE COMPANIES BY REGISTERED-OFFICE POST TOWN · COMPANIES HOUSE REGISTER, AUGUST 2026
SIC 43999 companies, as leads
Live rows from the enriched register. Email and phone values are withheld until you sign up.
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About SIC 43999
How many UK companies use SIC code 43999?
62,240 active UK companies list 43999 (Other specialised construction activities n.e.c.) among their registered SIC codes. Each company may register up to four. Of those, 47,320 put it first. The figures come from the August 2026 Companies House register snapshot, and count active companies only.
Should a multi-trade builder use 43999 or a specific trade code?
If one trade brings in most of your income, use its own code. That means 43210 for electrical work or 43220 for plumbing and heating. Specific codes read better to insurers and merchants. Genuinely multi-skilled firms use 43999 or 43390, or list up to four codes covering their main trades. The choice is yours. Companies House records it without judgement, and you can change it on any confirmation statement.
Does my SIC code need to match my trade qualifications or scheme memberships?
There is no formal link. Gas Safe registration, NICEIC enrolment and similar schemes are checked on their own registers, not at Companies House. Matching the code to your trade is still worth doing. Customers, insurers and finance providers do look at it, and a mismatch invites questions. If the business changes direction, update the code on your next CS01 confirmation statement.
Find UK SIC 43999 companies
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