admission in UK university for Masters/ PHD program
In many UK universities, a minimum requirement for admission to a doctoral programme is:


an upper-second-class or first-class undergraduate degree; or
a Master's degree.


And even if it is not a minimum requirement for admission, it is almost certainly a minimum requirement if you want a funded place.

Significant professional experience may mitigate poor prior academic attainment, but I am not convinced two years would be enough to compensate for a third-class undergraduate degree.

If you are happy to self-fund PhD studies, I suppose there is no harm in having a go at applying for a doctoral programme immediately (although I would recommend making at least one application for a Master's, in case nobody accepts you for a PhD at this juncture). But, if you want funding for PhD studies, you will almost certainly need stronger academic credentials than you have currently.