Weird nobody else is irked that the soldiers seemed to fold the way they did. On TV apologizing within a few days, not they have nice suits on shaking the Iranians hands and apologizing.
In the days when conventions of warfare were observed, then it was OK to show the enemy the stiff upper lip and spend the whole time in captivity rattling off your name, rank and serial number.
Things are a lot different these days. The enemy will happily flout international law and torture prisoners, and so will the West.
I think the Guardian asked the same question that you did (and it is a very, very good question; I was very surprised to see Royal Marines being so cooperative)
An MoD chap had this unofficial statement on what military personnel should do when captured.
"If captured, tell them whatever they want and say whatever they want you to say. Any information that you have will be out of date before they have a chance to act on it, and anything you say we will just retract later, saying that you were obviously speaking
under duress. It's not clever and it's not brave to die rather than say something that cannot possibly help them anyway."
I imagine that this doesn't apply to Special Forces units, since one would hope they would be working with fairly up to date information when captured.
The official line is that the decision is left up to the soldier.