Sorry, I had to switch to laptop.
He's not a terribly popular politician in the country at large anyway, so it's not exactly unsurprising to see he's unpopular in the forces. More specifically, though, he's supported prosecution for people involved in Bloody Sunday and meets with extremely dubious people (incl. IRA and Islamists) out of a misguided and rather self-important sense of being a peace-broker. He's also been attacked far and wide in the press - sometimes perfectly legitimately, sometimes not-so-legitimately (e.g. his choice of coat or how deeply he nodded his head at the cenotaph).
Like I say, though, his popularity in the army isn't and shouldn't be important on this. This is not something soldiers should be doing. Evidently the army agrees, as they're investigating the incident and have called it an error of judgement.