So how do the two schemes differ?

Public-Private Partnership Government's preferred option, under PPP London Underground (LU) would hive off Tube's infrastructure - track, tunnels, signals and stations - to three private "infracos" for 30 years One would be responsible for Bakerloo, Central and Victoria lines; one for Jubilee, Northern and Piccadilly lines; one for the Circle, Hammersmith and City, District, Metropolitan and East London lines Government would then hand control of Tube to Transport for London (TFL) which is accountable to the Mayor of London Operation of trains would remain in public hands, under control of LU Infracos would embark on £13bn modernisation programme over 15 years. Each would receive regular payments from LU but risk fines if they fail to meet targets Finance would be divided between government subsidy (45% in first 7.5 years), LU revenues (30%) and private finance (25%) Timetable for first 7.5 years would include 60 miles of track replaced and repaired; 500 refurbished or new carriages; 50 stations modernised; new signalling on Victoria and Northern lines; CCTV in trains and stations Work would continue over following 7.5 years, but no details exist Arguments for: Government has used private finance to fund building of new hospitals and prisons. Enables large sums of money to be raised without affecting government borrowing Arguments against: TFL says might be difficult to enforce contracts if private companies opt to pay fine rather than undertake work

Bond Issues London Mayor Ken Livingstone's preferred option, under bonds scheme London Underground (LU) would pass to control of Transport for London (TFL) but remain as a single, publicly-owned entity under "united management control" TFL would set about raising £12.75bn funding for modernisation over 15 years Fund raising would be divided between fares revenue and government grant (64%), bond issues (34.3%), and rest through existing private finance initiatives Priority improvements would focus on factors which cause "most system failures": rolling stock, signals and track This would include mechanical refurbishment or replacement of 85% of rolling stock within 7.5 years; signal improvements at "pinch points" and track improvements where needed The second stage of modernisation would deal with expanding Tube to cope with expected increase in passengers, and improvements to existing stations Arguments for: As head of New York's Subway, Bob Kiley, now the boss of Transport for London, used bond issues to successfully improve the service. Bond issues have been used to raise money for the Channel Tunnel Rail Link Arguments against: The government cites delays and other problems with the publicly-funded Jubilee Line extension as a reason for separating big programmes from public funding