The UK workers have not made the same claims against the company as the Unions are attempting in Spain. OSM UK is paying staff according to the furlough scheme, and like thousands of other UK based airline crews this appears to be the norm, people are accepting it, at the moment, even BA has indicated it will provide only the minimum severance pay, not enhanced redundancy packages.
The unions in Spain are trying to insist the crews there were de facto employees of NAS and thus entitled to certain termination conditions according to Spanish employment laws.
Forgetting the A-typical employment practices, the UK are used to this type of "agency agreement" and as far as we know no pilots are trying to go down a similar route to the Spanish.
At the end of the day the UK jobs have gone and if the crews can at least get something that's better than nothing. The rest of Europe appears to be paying circa 5000 euros a month whilst the companies furlough, but it varies from state to state