Hi Ash
A couple of suggestions if I may?
Firstly, ask your boss for an appointment to discuss it. Explain that you know how busy he is, but that you would value 30 minutes of undisturbed time to discuss this important matter.
Secondly, completely forget what other people earn. This is all about you and the value that you bring to the firm.
Speaking as an employer, the moment any employee starts to talk to me about what their colleagues earn, I turn off completely. The prime reason is that I can't discuss it - what another employee earns is confidential to him/her, and I can't say things like "yep - you're right, it was a mistake to give Joe that payrise last year, because he really doesn't deserve it." When employees discuss pay they often don't differentiate between before/after tax, the effect of Working family tax credits, overtime and all sorts of other things so their beliefs are often wrong. But I can't break confidenitiality to put that error straight. I have employees that I think are over paid. We all make wrong judgements sometimes, and when an employer does that, since it is almost impossible to cut someones pay, the result is an overpaid employee. Assuming that they aren't terrible (just over paid) often the best solution is just to let inflation eat away at it over a few years.
Over paying an employee is an expensive mistake. But overpaying an entire workforce in order to maintain what people think are "correct" differentials in comparison to that overpaid employee is the road to bankrupcy.
In my experience, employees get very uptight if they think that something is "unfair". But I run a business to be profitable, not to conform to a third party's idea of what "fair".
Just my 2 pennoth.