Yes, I work for the Jobcentre network but I work closely with very experienced doctors who spend every day listening to people explain their 'disabilities'. Let's take depresssion as an example again. I had a bad episode of depression a few years back so I know of what I speak.
When you have clinical depression you are totally f***ked. You can't function in any meaningful way. I couldn't read a book, watch a TV programme, play a game of cards, hold a conversation or indulge in my favourite pastime of playing guitar. No interest in these things and completely unable to concentrate on anything for more than a few seconds. Six months of hell and two years before I could really say I was better. Even now I know the black dogs are lurking waiting to pounce.
The doctors tell me that they see countless hundreds of people signed off by their GP as suffering from depression. When they ask them how their depression affects their daily life they are met with blank looks. Apparently many people suffer from severe depression without it affecting their life in any noticeable way. They will happily say that they spend their days surfing the net, playing X-box, watching TV, reading, going for walks, meeting friends etc. In other words doing all those things that truly depressed people are incapable of. Their GPs are more than happy to issue sickness certificates because it gets these people off their backs.
These people are leeches. And there are a hell of a lot of them. I won't even begin to talk about 'bad backs'. And I'm basically a socialist.