Part-timers working same hours as full-timers for part-time pay

[Snaptheirfingers]

This is a Covid-19 situation. We are key workers (UK civil servants). Our normal work can't take place at the moment. So we are doing other jobs in similar roles to cover those off shielding and to keep us working.
The issue is that I work 3 days a week and am being asked to work 1 or 2 days a week on my normal pay, so a bonus of a paid day off though I never know when it is until the evening before. My colleagues who are full-time employees are also being asked to work 1 or 2 days. They get their normal pay too. We are just on the minimum wage so I worked 2 days this week and would have earned about £100, my colleague also worked 2 days and got £250. I know this is short lived we may be back to our normal jobs and days next year but it doesn't seem fair! A fellow part-timer raised this with her line manager and has suffered as a result (not being selected for interview for a promotion).

Isn't this happening all over the place though? In my workplace there are people who have been furloughed and people who haven't.

There are people working who earn less than the people who are on furlough simply because that is their contracted salary. They can't just turn around and say 'well X on furlough earns £10,000 a year more than me usually and so I want their wage whilst I keep working'.

They are paying you the same salary they always have. You aren't losing anything.

given high risks of redundancy would much rather be working than furloughed as it could well be an indicator of who is more likely to be kept on or let go.