It is entirely possible to earn that much (and more) in London, outside of London - assuming you're not in a complete backwater that much should be possible. I

It is entirely possible to earn that much (and more) in London, outside of London - assuming you're not in a complete backwater that much should be possible. I'd say rather than worrying about what technology you know, spend a bit of time focusing on the business side - how you find and attract clients, how you negotiate, what business areas you target etc. It is likely that the clients you are dealing with have unrealistic expectations of what engineering costs.