Re: I cannot understand the merits of this case
Uber is acting as a marketplace - it brings service providers and potential customers together, and takes a fee for the privilege. As part of this, it may or may not choose to put measures in place to ensure that a satisfactory standard of service is being offered, as that protects its own reputation and therefore business.
It seems therefore that it is entirely valid to compare it to, say, eBay, which does exactly the same thing. If I start a business selling goods on eBay, and earn enough to make a living, that emphatically does not make me an employee.
The only difference is that in the case of eBay, payment is earned for selling items, whereas in the case of Uber, an argument could be offered that this is more of a personal services scenario. But it isn't - a driver is not being paid for their time per se, but for the fact that they have completed the service that was required, i.e. to move people from place to place. If they drive more slowly, they will earn less. This is not how employment works.
Please note that I makes no difference to me one way or the other - it just seems so clear cut that I genuinely don't understand how the GMB feel that they have any legal basis to their case.