Can I work another job while earning the 80% job retention?

Actually after reading through some other sources it seems to only specify you can't work for the employer who furloughed you so you're right enough (for the time being at least).

Working for other employers. Will workers be able to work for other employers while furloughed? This seems possible, because the details released so far simply say that the worker cannot do any work for an employer that has furloughed them. If workers can pick up work elsewhere while still being furloughed, it will make it more attractive. We expect the government shortly to confirm the rules concerning working elsewhere during furlough.

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