It's perhaps fortunate for Cameron that his mucky attempt to support a ban on the wearing of the crucifix at work will not be binding on the Sovereign. The opening of Parliament would look infinitely less rich if the Queen were to wear a baseball cap, say, in place of the crown. For at its apex is a ball, representing the world. Above that is a cross. The motif is repeated in the Orb of State. The message is clear enough; Christ reigns above the temporal authority of the sovereign. The crown, and the cross, are ubiquitous in our society; on postboxes, in courts of law, on the helmet plates of police officers, on the rank insignia of officers of field rank or above, on regimental and naval crests, on our debased coinage. Our gallantry awards are crosses. The flag of England is Christ's cross. The symbolism is anchored deep in our national psyche, but hardly anyone notices it.
Ban the tiny gold crucifix worn by many Christians including soldiers in battle and you deprive them of the succour of the faith in the event of unexpected death - the reason many wear one. It's display tells the emergency services or the triage nurse that an ordained priest may be summoned, to administer extreme unction to Catholics; penance, anointing and Viaticum ('provision for the journey'). The anointing with oil echoes the anointing of a new Sovereign at the coronation, and for the same reasons.
I suppose Cameron could cause all those devout nurses and airline clerks to have the crucifix tattooed on their breastbone instead, but surely even Dave can't be this crass?