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?

Whether workplace managers alone are enough depends on how recently you graduated. If you finished your degree within the last 2 to 3 years, most UK universities still expect at least one academic reference alongside any professional one, especially for research-focused Master's programs.

Reference Requirements by Your Timeline

How to Strengthen Your Reference Mix

• Check the exact entry requirements page of each program, wording varies between two academic and one academic plus one professional.
• If possible, submit one professor plus one manager for a well-rounded profile.
• If you have lost touch with a professor, email admissions directly and explain your employment timeline.

My Advice

Reach out to your former professors now, even a short email, since it is far easier to secure that reference before more time passes. If you genuinely cannot track anyone down, contact the university admissions team directly and ask in writing whether two professional references will be accepted instead.