In conjunction with the works to integrate the two lines, two major extensions were undertaken: northwards to Edgware in Middlesex (now in the London Borough of Barnet) and southwards to Morden in Surrey (then in the Merton and Morden Urban District, but now in the London Borough of Merton).
Sammen med arbejderne om integrering af de to baner, blev to større forlængelser anlagt: mod nord til Edgware i Middlesex (nu i London-bydelen Barnet) og mod syd til Morden i Surrey (dengang i Merton and Morden Urban District, men nu i London-bydelen Merton).