If employer offered London weighting then the commute to work would not be as expensive, so london weighting could be an argument of T&C e.g. crew who are Manchester based should they be on same Basic as crew who are London Based ?
I give up! - Did you know when you took the job that London weighting was not offered?
Here is an alternate view point for you:
If I worked the hours that you do my
total salary would, without question, be less than yours. That is with over 20 years experience and an EASA Engineer's licence.
You could quite easily be working in a job you hate 9-5 Monday to Friday for quite a lot less money than you earn. There are millions that do. Just look at what you do have and remember that before you vote for a strike and potentially lose either yourself or others their jobs.