It depends on whether it's frustrating to you or not. Fifty percent isn't bad, and as you're working, your full attention probably isn't on our anyway. It gets you used to the sound of the language, which may help you when you're working on your own pronunciation. My suggestion would be to write down some words you don't understand that seen to be popping up a lot. Look up the definition, study those words. When you're comfortable with them, listen to that same podcast again and see if you understand more of what's being said. I might also suggest listening to a podcast where people are speaking more casually, since you can pick up more of how people really speak. (The news can be really formal, so I found that sometimes it didn't prepare me for accrual conversations with native speakers in my target language)

Shima, I understand that you have the radio on while you work - it that correct? If so, are you actually paying attention to it, or is it background noise? If it's basically background noise, it won't help you any more than having (for example) classical music playing.

I think it's better to find a podcast in english for children. The words will be more easy but you learn how to sentences work. I do not live in England, so I hope the next one who is answering this question does and gives you a link to this podcast.