At the moment I have full time job at DHL and I'm considering to have a second full time job for some time! My question is - Can I, by law, have a second full time job if my working time don't overlap?

You will need to have authorisation from your current employer for this and you will also be paying BASIC rate tax on any second job.

In all honestly I don't think it's realistically possible to hold down 2 FULL time jobs.

You do need to check your current employer's policy on second jobs. Where I work, it is not disallowed unless one works for a similar agency doing similar tasks. Competition.

But as long as I would not overlap duties and would continue to maintain a good quality job performance on my first (primary) employment, all is well.

However, the caveat here is my employer's perception of how the second job is affecting my job performance on my primary job.

I do work full time and part time. It was a big deal since I had to provide documentation that the second job was not going to interfere with my primary employment. Even the second employer was called and asked questions about the job duties and expectations.

If you do this, do it right and go through all the proper channels. You do not want to go behind your supervisor.

I do know some people who have two full time jobs - one of them is a guy who lives above me. He meets himself coming and going. His wife says she hardly sees him. But for them, it is financial reasons he does this. She works too. So it is possible but I wonder how long a body can take that kind of stress.

That would be my main concern - your health, both physical and mental.

If you can do it, there is no restriction to having any number of jobs. For example I am a Pastor and a medical tech, plus a few other things I do.

Before even thinking about extra work, check with your existing employer. Some firms have clauses that set out rules for second jobs.

Be sure your employment contract doesn't say anything about you having to be available after normal work hours. If it does, that might limit your ability to take on other jobs.

Sometimes there are clauses to stop staff from working for a competitor.

Don't take on another jobs that could bring your employer into disrepute. An example would be if you were a public figure working as a stripper.

There isn't anything illegal about working 2 full-time jobs, but, on a practical level you need to consider the physical toll that a second job can take.