I don't fly airbus so what happens in their FMC's may be completely different i just don't know.
However in Boeing aircraft you have a cost index (if im preaching to those in the know i do apologise, but not everyone on here knows what a cost index is) which changes the various speeds depending on what you set in the FMC. In the 73 classic you can put any number in from 0 to 200.
The way i understand it 0 is min fuel usage and 200 is max speed and all variations inbetween. As the price of fuel goes up airlines are using lower and lower cost indicies. The lower the cost index the lower the speed in the descent. My airline have been told to use a low cost index and then ammend the descent speed to 280 knots to keep a good speed above fl100. I'm just guessing here but perhaps several uk airlines are telling their pilots to ammend their cost index to a lower setting and not to change the descent speed in the descent. Just a guess.