OK, I realize that MPs aren't going to follow human rights legislation to the "T", I take your point and tend to agree with you, but...
It is not legal to ask someone how old they are when they apply for a job. You may ask if they are legally allowed to work at the job you hiring for. So for a more mainstream example, if you are hiring a bartender, you can't say "Are you 18?", you may ask if they are old enough to legally serve alcohol. Most jobs with age restrictions need some kind of licence which should cover most situations. But it's not legal to ask if someone is 21 if it is legal for an 18 year old to do the job.
That doesn't excuse anything that happened at BP, I am just commenting on the point you brought up.