Slack is the most widely adopted team messaging platform in UK startups. It's built around channels — topic-based chat rooms that keep conversations organised — with real-time messaging, file sharing, voice and video calls, and a search that actually finds things. Its ecosystem of 2,600+ integrations (Google Drive, GitHub, Jira, Xero, and more) makes it the central hub for team communication. The free tier is genuinely useful for small teams, while Pro (£7.25/user/month) unlocks unlimited history and integrations.