Am I right in thinking that I fill in the name, address and NI number on the
> P46 but do not sign it.
Why would you not sign it (if needed?)
I then continue to pay standard PAYE on the main job, and have full basic
> rate tax deducted of this second income (which would be correct as I would
> get my full allowances from my main job)?
Yes.
Would this cause problems at the IR? - i.e having two jobs/two tax codes > etc?
No.
Would my main employer need to know about this second employement (from
a tax perspective - not a contract of employment etc issue), would the local
> tax office inform them?
No.
If as a result of having two jobs you find that you overpay tax (its possible) then you will be entitled to a tax refund at the end of the tax year.
Regards Sunil