There have been US law firms in London for many years. A lot of them have struggled to grow and then maintain consistent strength against strong competition from other incomers and from the indigenous UK firms.

Now a batch of firms seem to have cracked it.

They have done it by keeping their practices in London aligned with the natural strengths of the firm back home. Using "Power alleys" has allowed the firms to create synergy with existing practices and build strongly in London.

The same approach works for any firm building a new office in a new location.