Employment under TWES

[cyberwiz]

Hi,

I have an 18 month TWES permit and have been working as a trainee for 7 months now, and my initial contract with the company is about to expire. I wanted to enquire about becoming a full time employee with the company, but am unsure of how this will play out at the end of 18 months, as the TWES requires you to leave after 18 months. So I have a couple of questions I'd appreciate the answer to:
1. Can you change job roles and employers under the TWES?
2. Is there any possibility to stay on in the UK after the TWES expires?
3. Would I be eligible to apply for the HSMP under a TWES permit?

Thanks a lot!