An SEO agency provides a team of specialists — technical SEO, content, link building, strategy — for typically £1,500–£5,000/month. An in-house SEO hire costs £35,000–£65,000/year in salary (£2,900–£5,400/month) plus tools, benefits, and management time. For most UK businesses spending under £5,000/month on SEO, an agency typically delivers more breadth of expertise per pound spent. For businesses with significant ongoing SEO needs that require deep brand integration, strong content operations, or rapid in-house iteration, a senior in-house SEO manager (supplemented by an agency for specialist tasks like link building) is often the optimal model.
The agency vs. in-house question is often framed as a binary choice — but the most effective setups for medium and large UK businesses are frequently hybrid: a senior in-house SEO lead who owns strategy and direction, supplemented by agency specialists for technical execution, link acquisition, and content production at scale. This combines the brand knowledge and continuity of in-house with the specialist depth of agency.
When an SEO agency is the better choice
- Your SEO budget is under £5,000/month — a senior in-house SEO hire costs this much in salary alone, before tools or production
- You need breadth of specialist skills — technical SEO, content strategy, link building, and analytics require different expertise that one person rarely covers deeply
- You are scaling quickly — agencies can flex resource up or down as needed; headcount changes are slower and more expensive
- You want to test SEO before committing to in-house — agencies provide results data that justifies in-house investment with evidence
- You are in an early growth stage — an agency provides strategy and execution without the management overhead of employee administration
When in-house SEO is the better choice
- You have high content needs that require deep product or industry knowledge — an in-house person learns your business in ways agencies cannot match
- You need SEO closely integrated with product, sales, and engineering teams — physical or regular proximity enables collaboration that remote agency relationships cannot replicate
- Your SEO programme is at sufficient scale to justify dedicated headcount — typically when agency costs exceed the salary equivalent
- You have had poor agency experiences and need accountability within your organisational structure
UK SEO manager salaries in 2026: SEO Executive (0–2 years experience) £25,000–£35,000; SEO Manager (3–5 years) £40,000–£60,000; Senior SEO Manager or Head of SEO (5+ years) £60,000–£90,000; SEO Director (strategic leadership) £85,000–£130,000+. London salaries are 15–25% higher. Add employer National Insurance (approximately 13.8%), pension contributions (minimum 3%), tools (£500–£2,000/month), and management time — total cost of an in-house SEO Manager is typically 1.3–1.5× salary. An agency charging £2,500/month provides more specialist breadth than a £40,000/year in-house hire for many business types.
Evaluate SEO agency performance against pre-agreed KPIs: organic traffic growth (monthly vs. comparable period last year), target keyword ranking improvements (top-10 positions for defined terms), organic leads or revenue generated, domain authority growth (Ahrefs DR or Moz DA), and content production volume. Monthly reporting should show clear progress against these metrics. If after 6–9 months of engagement you cannot see clear progress in at least two or three of these areas, the agency is either under-resourcing your account, applying an ineffective strategy, or both.