When you read about an impending dangerous volcanic eruption near a populous city in the Daily Mail, it's OK to be dubious. The Daily Mail, despite its voluminous output of articles (frequently and happily featuring lovely women in bikinis, lingerie or even not wearing a THING), isn't a definitive source on scientific topics. (But it has occasionally brought scientific topics to my attention, in between the bikinis.)
Such is the case here. Even though the Daily Mail breathlessly hyped the possibility of a volcanic eruption near Naples, it is grounded in reality. Becausue the area around Naples is volcanically active, it's entirely possible there will be another eruption there eventually.
Well, eventually might not be as far off as the Neopolitans would like. Because that Daily Mail article is reporting basic facts, similar to the Science Digest article linked below.
Campi Flegrei Volcano eruption possibly closer than thought
"By studying how the ground is cracking and moving at Campi Flegrei, we think it may be approaching a critical stage where further unrest will increase the possibility of an eruption, and it's imperative that the authorities are prepared for this," explained Dr Christopher Kilburn, Director of the UCL Hazard Centre."(UCL = University College London)
So, it is possible that the Naples caldera could be gearing up for an eruption in a future that is nearer in time to the present rather than it is to the farther future. In other words, it could be getting ready to erupt soon (soon in the geological sense could still be within a century, but still...)
The last eruption in the region was 1538, which built Monte Nuovo, shown below (and a locator map below that),