What is a reasonable pay increase in this situation?

[Delectablenectarine]

To give some background, I was hired as a junior over a year ago for a specific role. After a few months, the opportunity arose to take on an additional role (not my main role but it still takes up significant time). I received a pay increase of 3k for this year. Now another role has come about due to someone leaving. I have been looking after their role in the meantime but was approached to do it all the time in addition to the two roles I’m currently doing, this will also take up significant time. I was told that this role would be reflected in a bigger bonus this year and an increase in my salary next year. I saw the role advertised for over 30k but it was for a more experienced candidate, of which I don’t have loads of in the area. Wondering what a reasonable increase for this would be so I’m prepared to negotiate? Thanks in advance

So you're being asked to do the advertised role plus your original FT role and another piece of work (FT?) on permanent basis ?
Id be expecting at least the £30k that the advertised role quoted, plus additonal resource to support with the additonal responsibility.

If you are going to do the job then you deserve the salary it attracts. You say that you don't have experience but you do. You are doing the job right now. You will be doing it for the 2-3 months that it takes them to recruit someone.

If you are doing it well then you have valuable experience. Someone new to the organisation is going to take a couple of months to get up to speed. You are already up to speed.

If you are good enough to do the job then you are good enough to earn the salary.