I've instructed on then until recently. Unlocking of the doors while the train is in motion has been prohibited on all classes for some years now as it is deemed as equally dangerous as locking people inside a carriage. Have a read of page 11 of the Railway Group Standard;
http://www.rgsonline.co.uk/Railway_...ck/Railway Group Standards/GMRT2473 Iss 2.pdf
This paragraph in that document stands out:
" B2.2.2 Action to bring existing power operated external doors into compliance with the requirements of this document is not required ".
I can assure you implicitly that on any 14x or 15x unit that the opening of any exterior door is not contingent on train speed and would occur whether at 0mph or 75mph. The only unit of that type that has any kind of delay is the 158/159 which has a crude delay mechanism whereby once the egress plunger is activated train wire 4 is immediately broken initiating an emergency brake application, then the time taken for the air to drain from the door system (16-20 seconds typically) is the only thing stopping the doors being physically opened. Again this is the case whether at 0mph or 90mph. The low speed relay on these units does not affect the operation of foor circuits in any way.