As usual, it is "stupid passengers" who are to blame for their own problems.
BA Advice:
Following our advice to reduce the risk of DVT:
drink adequate fluids (BUT DON'T STAND AROUND WAITING FOR THE LAST LOO WORKING ON A 12 HOUR FLIGHT)
avoid smoking
avoid beverages which contain alcohol and/or caffeine both before and during the flight
avoid crossing legs when seated
walk around the cabin whenever you can (ER...BUT DON'T, OR PRUNE REGULARS WILL CALL YOU STUPID)
stand up in your seat area and stretch your arms and legs (IF YOU'RE A FOOL!)
carry out the foot and leg exercises advised in the Well Being section of the Highlife in-flight magazine, on the in-flight entertainment system and the Well Being section on ba.com
wear loose fitting comfortable clothes when travelling