What is wrong with an Identity Card ?
In Continental Europe, everybody has one and must carry it at all time. People are used to it and nobody complains.
The concept of compulsory identity papers or cards is one of the things that defines a citizens relationship with their state, in the UK the relationship, currently under huge strain, has traditionally been one of the state as servant to the people. I would suggest that in many European countries the relationship is fundamentally different, the state appears to have more power of the individual and the compulsion to carry your papers with you at all times is a manifestation of that power.
Most of us in the UK want to keep the government at arms length and preserve the concept that the state is subservient to the people, we don't want ID cards even if, and it's a big if, they provide a little more security.
Well done to BALPA for fighting this one, in my opinion it's almost worth the subscription on it's own.