To ask the Secretary of State for the Home Department what assessment he has made of the recent tracer gas trials in the Westminster area as part of the Department’s Chemical, Biological, Radiological and Nuclear Science and Technology Programme; what discussions he has held on further such trials; and if he will make a statement. (141700)

[holding answer 11 June 2007]: It is not clear what type of assessment the question refers to. The trial is ongoing and the results will be assessed in due course to improve our understanding of the movement of material in the urban environment.

Further discussions have taken place in respect of the planned second phase of the trial which will be undertaken in early 2008 following analysis of the first phase results.

We encourage the publication of research results but this may be restricted for reasons of national security.

To ask the Secretary of State for the Home Department pursuant to the statement of 17 May 2007, Official Report, column 46WS, on Westminster tracer gas trials, what non-toxic gases were used in the Westminster area as part of the Department’s Chemical, Biological, Radiological and Nuclear Science and Technology Programme. (141788)

[holding answer 11 June 2007]: The non-toxic gases used in the trial belong to the family of chemicals known as cyclic perfluorocarbons. The actual gases released are: perfluoro methyl cyclohexane; meta perfluoro dimethyl cyclohexane; and para perfluoro dimethyl cyclohexane.