Salary wise it is definitely best to get a PhD, the starting salaries can increase by around £10,000. Also you are more limited in your career options without a PhD. With one you will be promoted much faster.
I think even if you don't want a career in academia a PhD is well worth doing if you think you'll be able to motivate yourself. Otherwise you may be in a job in industry, watching other people younger and less experienced than you being promoted above you which can get frustrating.