Stansted is the designated UK RED ALERT APT
As to tad closer, a tad is 2nm G/C......
Reprogramming the boxes would take time, but only a few mins.
The moment the call to ATC that there was a problem the destination would be STN, with no input from EY.
Non aviation people in UK, include the SAS, not good to argue with them, the RAF escort, was also mandatory upon the RED ALERT.
glf