Complex sentence: Under Roman Abramovich's control, the club has announced that it wants to extend Stamford Bridge to around 55,000 seats; however, its location in a heavily built-up part of Inner London near a main road and two railway lines makes this very difficult.
Split into simpler sentences: Under Roman Abramovich's control, the club has announced that it wants to extend Stamford Bridge to around 55,000 seats. However, its location in a heavily built-up part of Inner London, near a main road and two railway lines, makes this very difficult.