1) It's hard. And it gets harder if you are older. No one will tell you the opposite.
2) It will probably not add to the career progression since the people who stay in the industry at the same place usually grow faster if they are smart enough. However, it will definitely boost your skills and help you become a top performer compared to your peers.
Downside - it's true - you'll lack people the bigger part of the management skills:
- Leader as an architect and someone building the teams - not in consulting, since you don't have this aspect at all. All the people who are hired are smart
- Leader as a beacon and a person motivating the teams - not in consulting, since the people are already motivated with high salaries and up or out policy.
- Leader as a project manager working effectively with the different parts of the organization - you can definitely learn this in consulting since it has a lot of client and internal politics
Answering your question - it really depends on what's the alternative. If you have a good progression now and you can grow as a people manager - I would probably keep as it is. Moreover, the UK consulting salaries are comparatively low nowadays.
If you want to grow your problem solving, project management and politics skills - would definitely go there.
I would try to negotiate it with the current company - leave for MBB, stay there for a couple of years and then go back with upside.