I'm not a lawyer either, Skyline but I'm not sure about being able to do as you suggest if you are an employee - you could as a self-employed contractor where there is a contract for services between the two parties.
The HMRC tests for whether employee or self-employed are things like:
Do you work regular hours hours decided for you by the employer? - or can you decide
Do you supply all the support materials required in the course of your work?
There's a longer list half way down this page.
http://www.hmrc.gov.u...nt-status/index.htm#1
As an employee, one is handling money on behalf of the employer and its the employer's money.
But if you reckon you are an employee, go back to my origianl point - Mrs Theatre-Owner, how come you haven't been dealing with the HMRC for me as an employee, paying the employer's NI contributions on my behalf, deducting the employee's NI and tax as HMRC says you must do? The HMRC aren't going to be too pleased for you, are they now? Tell you what, we agree a financial settlement between us and just part company.
Just to remind you, if you manage to pull this off without further ado, you must declare the earnings as 'self-employed' earnings with the HMRC - she's just as likely to shop you as not paying tax if you don't.