Thank you for your question.
The tax treatment of your redundancy payments paid by the former employer are not affected by your concurrent employment.
Since this redundancy pay is paid by the employer, it constitutes a severance package, and you are allowed to work while receiving that redundancy pay. Since you are now working for the temporary agency, and not the original employer, even though your place of work is at the originial employer's place of business.
The only thing that will be affected by your taking a job so soon after redundancy is that you might lose or have a greatly reduced job seekers tax allowance.
BUT the tax free status of the 30,000 will not change, simply because you started work with another employer:
the ONLY time redundancy pay is taxable is if the employer specifies a portion a payment for benefits. The benefits portion is taxable.