Need Gurus help-Supplementary employment

[msislam]

Hi Guru,
Please can you explain me about the supplementary employment in TIER 2 General?
Q1 : If I work for another company(B) for 20 hours at evening from remotely (same level and similar tasks that I am doing for Company A) then will it act as a supplementary employment.

Q2: Who will pay the tax company (B) or I can pay the tax .

Q3: Company B wants to make it 6 months fixed Contract. Because they are was my first TIER 2 Sponsor company and they want support from me and within 6 months they will sort out my gap.
company B proposing me to pay tax myself.

Your kind help will be highly appreciable and help me lot.

Regards,
Mr Islam