[As a Ltd company it seems you can opt out of the Agency Regs]
The difference is as a Ltd company most agencies are hiring the company not the person so therefore you as an individual remain an employee of the Ltd company not the agency. Therefore technically you never change employer regardless of how many different agencies you work for.
This is the reason some of the agencies/companies who employ the Ltd company personnel insist on seeing proof of public liability insurance as technically you can end up not being covered by the agencies insurance policy either.
Self employed workers have another whole set of rules to work to as you do not have to be a Ltd company to opt out of an agencies PAYE scheme you can work quite legally as a self employed person.
It appears to me at least that the whole tax situation is now down to personal choice.
For the best chance of a SED claim go PAYE. If you are not doing your days Ltd company is proabably the most tax effective way of legitimately avoiding tax.
However with the IR35 rulings you have to be careful as a Ltd company not to continuously work for the same employer as then you may as well be an employee in the eyes of the HMRC.
James has hit it on the head. Live outside the UK and work Outside the UK and do not pay UK tax.
Best advice go and speak to a few accountants and assess your personal position. They have upto date information and can best assess how to keep your money in your pocket. So we can all go out and spend our money in the UK and end the recession mmmmmmmmmmm………..