Contracts & laws in the UK

Hello everyone!

If there is someone who knows laws and working rights fir expats in UK, I would really appreciate if cou give me some info.
I have Romanian Nationality, but have Spanish residency and lived and worked in Spain in the last 6 years. At the moment I am negotiating a contract with a company based in UK, but the job is placed in Spain.
As i know, Romanians don't have working permit in Uk, but would like to know what happens in my case as i wouldn't work in the UK.
I checked with authorities in Spain and they told me that as my activity will be on their teritory should be applied tge Spanish laws.
What can you tell me? What opyions do I have?

This a very Internations issue :-)

Thank you in advance for your help.

Reards,
Ancuta