The text of the postcard reads:

"Dear Prime Minister,
I am deeply concerned about plans to develop and place weapons in space. Since current treaties on this issue are not far-reaching enough, I call on you and your government to:

1) Declare a UK ban on the development and deployment of weapons in space (including a commitment not to help others develop or deploy weapons in space)
2) Urge other countries to declare similar bans
3) Lead the way in negotiating a verfiable, multi-lateral treaty to ban space weapons and avoid a space arms race.

I would be grateful for a response detailing the steps the government plans to take to implement these measures."