Short answer: yes. WhatsApp messages, like emails, text messages and other electronic documents, are routinely relied on in UK construction adjudications, arbitrations and court proceedings. This is general information rather than legal advice, and the general principles are enough to change how you think about your site group chats.
Admissibility is the easy part
English civil proceedings take a broad approach to evidence: if material is relevant to the issues, it is generally admissible, and the argument moves to what it proves and how much weight it deserves. A message sent on the day, by a person doing the work, describing what happened, is classic contemporaneous evidence. The definition of a document in civil procedure is wide and comfortably covers messages, photos and voice notes.
In practice, site messages already appear in disputes constantly: to show when an instruction was actually communicated, when access was blocked, what conditions were found, what was agreed informally between people who never wrote a letter in their lives. Tribunals treat them the way they treat any record made before the argument existed: as more credible than recollections assembled after it.
The real battlegrounds: authenticity, completeness, weight
Authenticity. Can you show the message is what it claims to be: sent by that person, at that time, unaltered? Screenshots cropped from a personal phone months later invite challenge. A capture made at the time, preserving the message, sender, timestamp and the media attached, is much harder to argue with.
Completeness. A message pulled out of context is vulnerable to the neighbouring messages you did not show. If the thread is disclosed selectively, expect the other side to demand the rest, and expect scrutiny of anything that looks curated. Preserving the whole project thread is both safer and required: disclosure obligations in litigation extend to relevant electronic communications, including messaging apps, and parties are expected to preserve them once a dispute is in prospect.
Weight. Even authentic, complete messages vary in persuasive force. "Plot 2 shut again lads" supports a delay claim; a message with a photo, a time, an author and a clear statement of cause supports it far better. The evidential gap between chatter and record is the gap between what a tribunal reads sympathetically and what it relies on.
The practical problems with raw WhatsApp
None of the above requires special software, but the realities of site WhatsApp work against you. Messages live on personal devices that get lost, replaced and wiped. People leave and take their phones with them. Group history is subject to retention settings, including disappearing messages, which are a records disaster if enabled on a project group. Voice notes, often the richest evidence, are unsearchable audio. And eight months of mixed banter and business takes days of expensive time to trawl when a dispute finally lands.
So the sensible position is not "WhatsApp is fine" or "ban WhatsApp". It is: treat the project group as the evidence stream it already is. Capture it as it happens, preserve it completely with its metadata, transcribe the voice notes, connect the photos to their context, and structure the lot into a record you can actually search when it matters.
What good looks like
A project record built from site messages should preserve the original alongside the structured version: the diary entry that says the pour finished at 14:20 links to the message, the photo and the transcript that evidence it. Entries are timestamped and attributable. Nothing is edited after the fact. Retention is set deliberately to match your contractual and limitation periods, not left to whatever a handset happens to keep.
That is precisely what Construction Metric does with the group chat your sites already run. Nobody changes how they work; the record simply survives, structured, searchable and ready for the day someone asks you to prove it.