The reason why they are scams is because the work doesn't really exist like this in the UK anymore. No doubt there will be a few exceptions.
Data entry work, and other computer work of this type (and I'm talking about transaction type computer work, not development of simple programmes, databases, macros, which requires some thinking) can easily be outsourced to places like India where qualified people will do it for a pittance. Certainly the UK minimum wage or less.
There ARE jobs like this in the UK, but they do not come via third party websites - they come from businesses and organisations knowing someone directly. They best way to access it is picking up the phone and cold-calling, but expect it to be a long haul / very miss-and-hit.