I'm still a little unclear what your asking but here goes.
This tally's reasonably well with my own experience. I've spent a lot of time in the mountains of the UK (Mainly Snowdonia in North Wales where I live). My long term ambition is to move into more alpinism type route in France, Germany, etc. (much like yourself)
As such I'm going to answer your question slightly indirectly and tell you what I've been doing to get up to where I wish to go (and this will hopefully help you too)
I've been rock climbing for a number of years. This has helped me develop a number of skills that you will likely need for alpine days, specifically:
- Rope skills
- Making belays
- Moving on rock
- Placing secure anchors
I knew though that these skills likely weren't enough for what I wanted to do. So my next step has been to get some winter training (the Alps are obviously covered in snow and ice so this is very important).
I actually looked into doing a winter skills course in Scotland but found these prohibitively expensive. So I decided to teach myself (this isn't for everyone, I'm a bit of a nerd on these types of subjects and I like to think I'm aware of my own limitiaions).
so I bought the following items:
- Ice Axe (walking style not climbing style)
- B2 rated boots
- C2 rated crampons
- Ski goggles
I already own a full set of winter and waterproof clothing. I then spent the winter in Wales (when it snowed) walking paths I knew well and gaining experience. I practised self arrest and various other winter specific techniques that I could only do with snow.
We then spent a week in Scotland walking in the cairngorms (ticking off munroes). I'm now pretty confident up to winter Grade II.
I don't feel (TBH even after all of this practice, etc.) that I have enough skills to tackle the Alps quite yet (I also can't afford it right now as I'm trying to save to buy a house). I have not done any crevasse rescue or work on glaciers (because there aren't any in Scotland).
I would suggest that Mont Blanc (via the ordinary route I think it's called, the most common one) is typically everyone's first Alpine mountain and you will struggle to find any other peak as accessible (with a guide). So I can't really suggest another European hill to do as training. There are numerous less busy alternatives though, Mont Blanc can get very busy.
Obviously none of these mountainous areas are anywhere near London, I'm lucky I live in north Wales. But I would suggest spending as much time as you can in winter in Scotland, etc. this will help you hone you winter skills which you will need for a summer accent of Mont Blanc.
Interestingly I've just finished reading an article in the perils of alpine routes on Mont Blanc, prob worth a read http://www.ukclimbing.com/articles/page.php?id=7563