The verdict in three sentences
A custom client extranet for an accounting firm in London costs between £20,000 and £40,000 in 2026, with a 3-month timeline. It replaces scattered email and WhatsApp exchanges with structured document upload, automatic reminders and e-signature of engagement letters and accounts. With around 25 hours saved a month and hosting at about £150 a month, the firm recovers its investment within two years while securing client data.
The problem the extranet solves
In many London practices, client records arrive by email, WhatsApp or shared folders. A team member spends month-ends chasing bank statements, supplier invoices and payroll reports, then renaming and filing them. During deadline peaks (Self Assessment, VAT returns under Making Tax Digital, Companies House filings), this chasing becomes the firm's bottleneck.
The extranet gives each of the 220 clients a secure space with a monthly list of expected documents, an upload button from their phone and a dashboard showing what is missing.
| Module | Function | Indicative 2026 budget (£) |
|---|---|---|
| Secure client space | Login by email or phone, two-factor authentication | 3,000 to 5,000 |
| Document upload | Mobile photo, PDF, automatic filing by month and type | 4,500 to 8,000 |
| Automatic reminders | Expected-document list, email, SMS or WhatsApp nudges | 3,500 to 7,000 |
| E-signature | Engagement letters, accounts, board minutes | 2,500 to 6,000 |
| Firm dashboard | Missing documents per client, workload per staff member | 3,000 to 6,500 |
| Tax and payroll calendar | VAT, PAYE, Companies House reminders per client | 2,000 to 4,500 |
| Training and migration | Creating 220 accounts, client guides | 1,500 to 3,000 |
A core of client space, upload and reminders sits around £20,000. With e-signature, calendar and full dashboard, the project reaches £40,000.
Custom build or off-the-shelf software: the comparison
| Criterion | Custom extranet | Practice software (SaaS) | Email and WhatsApp |
|---|---|---|---|
| Initial cost | £20,000 to £40,000 | £0 to £3,000 setup | £0 |
| Recurring cost | About £150/month hosting | £25 to £60 per user per month | £0 |
| Fits your exact workflows | Yes | Partially | No |
| WhatsApp and SMS reminders | Yes | Rarely | Manual |
| Data location under UK GDPR | Your choice of host | Vendor's choice | On staff phones |
| Time lost chasing | 5 to 10 h/month | 10 to 15 h/month | 30 to 35 h/month |
These are 2026 orders of magnitude. Off-the-shelf practice software can suit a small firm of 40 clients, but beyond 150 SME clients with specific onboarding and chasing workflows, custom often makes the difference.
The 3-month plan
| Period | Steps |
|---|---|
| Weeks 1 to 2 | Scoping, document lists per client type, mock-ups |
| Weeks 3 to 7 | Client space, upload, reminders, dashboard |
| Weeks 8 to 10 | E-signature, calendar, security |
| Weeks 11 to 12 | Pilot with 20 clients, creating 220 accounts, training |
Mini case study
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Priya, partner of an accounting firm in London, serves 220 SMEs with 9 staff. She picks an extranet at £30,000 with e-signature, plus £150 a month of hosting, i.e. £31,800 in year one. The firm saves 25 hours a month of chasing and filing. Valued at £90 per billable hour, that is £2,250 a month, or £27,000 a year. Add 4 new clients won on the strength of the professional image, at £300 a month in fees, i.e. £14,400 a year. The project pays back in about 9 to 10 months.
FAQ
How much does a client extranet cost for a London accounting firm?
Between £20,000 and £40,000 in 2026 depending on modules. A core of document upload and automatic reminders starts around £20,000.
Will clients really use it?
Yes if upload takes one phone photo and reminders arrive where clients read them. In practice, 60 to 75% of clients upload on their own from month two.
Is e-signature legally valid in the UK?
Yes, electronic signatures are recognised under the Electronic Communications Act 2000 and UK eIDAS. The module costs £2,500 to £6,000 depending on the signature provider.
Where is the data hosted?
You choose: UK or EU hosting, with encryption and daily backups. A UK GDPR data protection assessment is included in the project.
What do hosting and maintenance cost?
About £150 a month for hosting, plus £300 to £800 a month for maintenance with fixes and support.
Let's scope your project. Tell us your number of clients, staff and accounting tools: we will price an extranet between £20,000 and £40,000, delivered in 3 months. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
