I would be surprised if a Bombardier solution would not be used as they supply LGW & STN and MAD (from a airport operator point of view).
Platform length would suggest the ability for 3 Car people movers as current models have the following specifications
Size : 12.8 metres (42 ft) length, 2.8 metres (9.2 ft) width, 3.4 metres (11 ft) height.