The man on the roof of an immigration centre in Lincolnshire is a Chinese national. Staff at Morton Hall near Lincoln said he took to the top of the 30 foot high building at 1130 BST.
Trained staff are on the roof trying to negotiate with the man who is not said to be making demands. Emergency services were on scene, although several fire engines have now left.
Lincolnshire police were called to a similar incident yesterday when a different detainee also got onto the roof but that was quickly resolved.
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Apart from a few showers, mainly in the morning, there will be a good deal of dry and bright weather.
Any cloud and rain will clear eastwards initially, leaving brighter conditions but also a scattering of showers through the day.
Rain possibly heavy at times. Relatively mild overnight.