You asked
The number of visitors to the London region, and the number of nights those visitors spent, for all available months in the past six years by country of origin and by purpose of visit.
We said
Thank you for your query regarding visits to the London region.
Information on visits to London over the six years to 2014 can be obtained from the International Passenger Survey (IPS) team. Special extracts and tabulations of visits to London broken down buy the other variables you request are available to order (subject to legal frameworks, disclosure control, resources and agreements of costs, where appropriate). Such enquiries should be made to: socialsurveys@ons.gov.uk. We recommend that you contact the IPS team via the Social Surveys email address in order to discuss your data requirements in more detail.
As this information is already available to you via this route ONS considers that S21(1) applies to this request and the information does not have to be supplied under the terms of the Freedom of Information Act. S21(1) is an absolute exemption and no consideration of the public interest test needs to be applied.
Hope that helps but happy to discuss further.