Depends on plants. I put 3 courgettes in today, they could suffer so I've put a cover on them... Some other stuff might be ok & it also depends how cold it gets in your spot. Forecast here is 3deg but site is well sheltered from N & W winds so plants might feel a bit warmer.
Apparently we're in for an 18 degree drop in the next 48hrs, should I be worried? We have quite a few young plants.