Dear Mr Rogers
Thank you for your email to Ken Livingstone on the subject of planning obligations. You may not know this but the provisions for entering into legal agreement for the interest of good town planning were introduced into planning in 1971, now known as s. 106 of the 1990 Town and Country Planning Act.
They are the principal means for securing town planning objectives that are set by elected politicians. The Mayor does not however have the power to enter into a s. 106 planning obligation but is very supportive when London Councils do so.
The use of planning obligations is defined by Government guidance called circular 1/97. In it, the Government makes clear that an obligation should be necessary (i.e. planning permission couldn't be given without it) and any benefit of it must relate to the developemnt under application is scale and kind. It is only when applications are deemed acceptable in the first place that a legal agreement can be entered into to secure provision which needs to be in place before the development can take place. The provisions are widely used for the procurement of new paving, bus infrastructure, affordable housing, public transport, land swaps etc etc.
The Mayor has published guidance on the scope of legal agreements in London which can be viewed here:- http://www.london.gov.uk/mayor/planning/docs/planning_obligations.pdf
The Mayor's support for tall buildings is because he thinks they are aesthetically pleasing and absolutely necessary to optimise the capacity of urban land. The context is that we have a housing crisis in the city and the most expensive offive rents in the world.
I hope you will find this informative. The point is that planning permission is not 'bought' as is suggested by your email and blog.