There are two services available from ÁTC for this scenario, DAAIS and DACS.
Designated ATSUs are responsible for the former, Danger Area Activity Information Service and are notified as such on CAA published charts; this information may not be included if you're using a chart from a 'private' supplier like Jeppesen.
DACS or Danger Area Crossing Service is also available from certain ATSUs which are radar equipped and are also notified on CAA published charts.
The above information is also in the UK AIP ,but I'm not sure if things like Sky Demon include it.
As Bigears said, simply ask the nearest ATSU if you're not sure.