Foundations
Part of Why professional services marketing foundations decide who wins clients
What to record before sizing the professional services marketing market
A guide to the assumptions and checks to set down before sizing the professional services marketing market, from boundary and buyer pool to illustrative spend.
| Case | Evidence or assumption | How it informs the estimate | Main limitation |
|---|---|---|---|
| Market boundary | Industry categories and a written scope | Defines which buyers and services count | Marketing is not an ONS industry category |
| Buyer pool | Official business counts and an England slice | Sets the number of potential buyers | Published counts cover the UK |
| Annual value | Spend assumptions by firm size | Converts buyers into estimated spend | The example figures are illustrative |
| Reachable audience | Personal information and lawful basis | Tests whether named contacts can be counted | Raw contact totals may overstate reach |
| Delivery capacity | Agency and in-house teams | Checks whether the estimated spend can be served | Capacity is a sense check, not a buyer count |
Choose the market boundary
Set the boundary before collecting counts. Decide which professional firms are in scope and whether the total includes agency services, in-house staff time, or both. The ONS organises statistics by industry rather than by marketing function, so firms buying similar support can sit in separate categories.
Solicitors, accountants and architects fall within professional, scientific and technical activities, while agencies serving them are classified under advertising and market research. Legal, accounting and architecture firms, along with engineering firms, also appear in different SIC subclasses. Record your chosen boundary before comparing figures.
Treat the result as a constructed estimate, not a published official total. State the inputs and identify the England market you intend to describe; the England market guide can help place the segments in context. A clear definition lets readers see what is included and challenge the assumptions rather than mistaking the calculation for an official statistic.
Identify the buyer pool
Start with the business population estimates 2023, then isolate the relevant industries and the England share. The estimates count UK businesses, not the professional services marketing market itself, so you need to set the boundary and extract the geography you intend to size.
The business population estimates are published annually and break counts down by legal form, employment size band and broad industry. They also distinguish registered and unregistered businesses. Choose which population to include, and use employment size bands rather than treating every business as a likely agency buyer.
The published figures cover the whole United Kingdom, so the England slice needs to be separated out in your workings. The ONS digital economy data can provide context for the digital-facing part of the economy, where search, paid social and marketing automation make up a large share of what professional firms buy.
Convert firms into annual value
For each size band, multiply the number of potential buyers by an assumed annual marketing budget, then add the band totals.
Exclude firms too small to buy support, or account for their in-house activity using staff cost, as appropriate. Keep the spend assumptions visible so readers can test their effect on the estimate.
Illustrative annual marketing spend
- £30,00012 fee earners
- £120,00050-person firm
Bottom-up estimate in five steps
- Take official business count by SIC
- Strip out firms too small to buy
- Apply annual marketing budget per firm
- Multiply firms by spend per band
- Add bands and check agency capacity
Use the illustrative spend figures as examples, not survey findings: a firm with twelve fee earners might spend £30,000 a year, while a fifty-person firm might spend £120,000. Replace those assumptions with figures suited to your estimate, then show the band-by-band calculation rather than reporting only a headline total.
Compare the result with the agencies and in-house teams available to deliver the work. If the implied spend is greater than local agency capacity could serve, revisit the buyer count or budget assumptions. Once the estimate is tested, the market entry checklist is a practical next step when considering entry.
Separate counted contacts from reachable audience
If a segment depends on named decision-makers, check what the law permits you to hold and use. The ICO explains personal information, which determines whether a named contact list can be used for targeting. Record the lawful basis for holding the data alongside the assumptions used to size that segment.
A raw count of named contacts can overstate the audience if you cannot lawfully hold or contact them. Check the rules before treating those people as reachable, and use the audience research guide when defining a segment. This keeps the estimated market tied to an audience the firm can actually approach.
Challenge the result before publication
Test the estimate against five points: the geography must be identified as England, the firm count should come from official business population data, and spend should use banded assumptions. Also record how data compliance was considered and include the assumptions table, rather than circulating a number without its workings.
A useful sense check is whether the estimated spend could be delivered by the agencies and internal teams in the area. If the figure implies more work than that capacity can serve, adjust the assumptions and explain why. Refresh the calculation annually, in line with the yearly business population estimates, and retain the earlier inputs for comparison.
