Yes Vintage ATCO, that means when the correction to the Sector Safe Altitude or Radar Vectoring Altitude (providing 1000ft obstacle clearance) reaches 200ft it needs to be applied.
Don't have the chart to hand but it does have to be icy cold. However, there have been times in the UK where the temperature has been below -10 over the last 30 years. Especially in Scotland where they do vector traffic from time to time.
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Chevvron,
Please have a read of the Flight Information Handbook next time you are in work. Altimeter corrections for the UK military are in there.
Regards,
DFC