The verdict in three sentences
A RAG-based AI assistant connected to 15 years of advice files costs GBP 50,000 to 140,000 for a 40-lawyer London firm, plus GBP 250 to 1,300 a month for the language model. The project pays off once document research time falls by 50%, which firms see when the corpus is clean and indexed by practice area. The non-negotiable condition is client confidentiality: UK or EU hosting, no model training on your data and strict matter-level access control.
What the budget for a legal RAG assistant covers
RAG (retrieval-augmented generation) does not teach your documents to the model. It retrieves relevant passages from your knowledge base, then asks the model to draft a sourced answer that links back to the original advice. Most of the budget therefore goes into preparing the corpus and access rights, not into the AI itself.
| Item | 2026 range in London (excl. VAT) | Comment |
|---|---|---|
| Corpus audit and regulatory scoping | GBP 6,000 to 15,000 | volumes, formats, practice areas, access rules |
| Cleaning, OCR and chunking of 15 years of archives | GBP 10,000 to 30,000 | Word, scanned PDFs, exported emails |
| Vector search engine and indexing | GBP 10,000 to 25,000 | client, matter, date and partner metadata |
| Matter-level access control | GBP 8,000 to 30,000 | sync with the firm directory and DMS |
| Question interface with citations | GBP 10,000 to 25,000 | direct link to source, Word export |
| Audit logging and dashboard | GBP 6,000 to 15,000 | who asked what, on which matter |
| Total project | GBP 50,000 to 140,000 | 2026 estimate |
Recurring costs include language model calls (GBP 250 to 1,300 a month for 40 users depending on usage), vector database hosting (GBP 200 to 550 a month on a UK or EU cloud) and maintenance at 12 to 18% of the project per year.
Confidentiality and hosting: the realistic options
The SRA Code of Conduct requires firms to keep client affairs confidential, and legal professional privilege must not be put at risk by the tools you use. UK GDPR and ICO guidance apply to any personal data in the files. Three architectures are on the table in 2026.
| Option | Indicative monthly cost | Confidentiality level | Watch point |
|---|---|---|---|
| Major US model API via UK or EU region | GBP 250 to 850 | adequate with enterprise contract | US data access laws |
| European model hosted in the EU | GBP 350 to 1,000 | high | quality varies on legal English |
| Open model on a dedicated UK server | GBP 800 to 2,200 | very high | maintenance and performance to own |
| Prompt retention by provider | 0 days required | essential | write it into the contract |
| Training on your data | prohibited | essential | mandatory written clause |
| Backup location | UK or EU only | essential | check sub-processors |
Access control is the most underestimated point. A fee earner with no access to a client's matter must never see an extract of it in an assistant answer. In practice, permissions are applied before retrieval, not after generation. Ethical walls for conflicts are mirrored exactly from your practice management system.
The UK has no single AI statute in 2026, but the SRA expects firms to supervise AI outputs. If you also advise EU clients, the EU AI Act generally treats this kind of research aid as limited risk: disclose that answers are AI-generated and keep human review before anything reaches a client.
Expected gains and honest limits
The main gain is research across past advice: finding how the firm handled a restrictive covenant in 2017 or a commercial lease question in 2021. Firms with a well-structured corpus measure a 40 to 60% drop in time spent. On the other hand, the assistant does not replace paid case law databases and may cite advice that a later ruling made obsolete, so every answer displays the source date.
Mini case study
Need a professional website?
Kolonell builds websites that attract clients, optimized for the Sénégalese market. Free quote in 2 minutes.
Olivia, managing partner of a 40-lawyer commercial firm in the City of London, estimates that 30 lawyers spend 2 hours a week digging through old advice. With the assistant, that drops to 1 hour. Over 45 weeks, the gain is 1,350 hours a year. Valued at an internal cost of GBP 110 an hour (not the billing rate), that is GBP 148,500.
Costs: a GBP 85,000 project, language model at GBP 800 a month (GBP 9,600 a year), hosting at GBP 500 a month (GBP 6,000) and 15% maintenance (GBP 12,750). Year one costs GBP 113,350, for a net gain of about GBP 35,150. From year two, running costs fall to GBP 28,350 a year.
FAQ
Is our data used to train the model?
Not if the contract explicitly prohibits it, which is standard in enterprise offers in 2026. Also require 0-day prompt retention and a list of sub-processors located in the UK or EU.
Can the assistant make up an answer?
The risk drops sharply with RAG because each answer cites its sources. Still set a rule: with no source found, the assistant says it does not know, and a lawyer reviews 100% of content sent to clients.
How long does deployment take?
Allow 10 to 16 weeks, including 4 to 6 for corpus cleaning. A pilot on a single practice area, employment law for example, can run within 6 weeks.
How many documents can be indexed?
A 15-year corpus often holds 80,000 to 200,000 documents. Initial indexing takes a few days, and each new piece of advice is added automatically within the hour.
Should clients be told?
A clause in the client care letter is recommended in 2026. It states that AI tools hosted in the UK or EU assist with research, with no disclosure of data to third parties.
Let's scope your project. Tell us the size of your knowledge base, your priority practice areas and your hosting requirements, and we will price the scope, the indicative budget and the rollout timeline. 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.
