For letters of recommendation, would workplace managers be enough or do I also need to contact professors from college to strengthen my profile in UK for a Master's?

Yes, workplace managers can provide strong letters of recommendation, especially if your work experience is relevant. However, for UK master’s applications, including at least one academic reference from a professor who knows your academic work is generally preferred and can strengthen your application.

With your Computer Science background and solid work experience, a mix of academic and professional references will create the best impression.