Max safe time in sun with no protection?

I'm in the UK and we finally have some sun. I work all day inside but often pop out and spend my half hour lunch break eating in the park.

If I forget to apply sunscreen to my body (i have some on my face always) is it still safe enough to spend half an hour in the sun?

My skin isn't super fair but also isn't tan. If I go abroad I sometimes burn a little but rarely burn here in the UK.