It's complicated.
Firstly, I don't believe that most people have in fact lost respect for the police, and I also believe that the vast majority of the public (myself included) accept that the police have an extremely difficult job to do, and are fully supportive of what they try to do, even if we don't always support (or understand) their approach.
Secondly, the fact that idiot like this 'gentleman' can bait the police and NOT get beaten up for his pains, says a lot about the way that the police behave - just try that in some countries...
Thirdly, we hear a lot about police misconduct, actions, failures etc because of the internet, just as we hear about a lot of things via the internet. The reach of instant communications has never been greater, and people can and do tell lies on the internet without too much fear of reprisals - newspapers have to worry about libel action, internet posters can generally get away with almost anything.
But, there's no doubt in my mind that although most of the public continue to fully support the front line police, their own bosses don't. Budget cuts result in less training, less equipment, a reduction in immediate backup and low morale, and in turn this can lead to police officers waiting for backup to arrive instead of putting themselves into dangerous situations, which can mean that things can get out of hand.
And some senior officers now seem to see themselves as spin doctors, being very economical with the truth when the police have screwed up, and often lying through their teeth, to protect the reputation of their force - when all that is actually needed is an acceptance that, sometimes, their officers don't get it right. Reasonable members of the public fully accept that police officers, like all other people, can't get it right all the time. What we cannot and will not accept is the lies and cover ups.
How do the senior police officers get away with lying? Easy. They know that complaints from the public will be investigated by their own internal investigators, and they know that their professional standards department only find that junior officers get it wrong, senior ones always get their full support.
As for the post above about police misconduct at demos, unfortunately this is by no means an isolated incident. Somehow, many police officers seem to be spoiling for a fight at demonstrations, and again their actions are covered up by their 'superiors'.