No, the filter is not safe!
No filter is "safe," if you fear health effects then do not use the filter. Please do not use a mask's article or talk page to discuss the safety of a filter.
The General Civilian Respirator was issued to every civilian by the government in the late 1930s and early 1940s. Civilians were legally required to have their gas masks within reach at all times, and there was an extensive propaganda campaign designed to increase awareness.
In fact, women had special handbags where they could carry their masks. After the war, unfortunately, many of these masks were cut, at the filter end to make an elastic band which was used as a makeshift slingshot by children.
This mask is very basic and does not even have an exhale valve. The air is breathed in through the filter and exhaled from the sides of the mask. The mask later developed to have an exhale valve, in the form of a 'flutter type' valve. Some of these masks had an arsenic 'pre filter' which was a green part which stuck out on the filter.The straps of this mask were very basic and simply went over the head (3-pointed harness). The length of the straps could be changed by removing the safety pins and replacing them when the desired length was reached. For vision a thin plastic sheet was placed providing frontal vision only.
This mask was issued to many countries who were allies with the British Military such as; Malta, Canada and New Zealand, all having their own variations (except for Malta). It was made by two main companies Seibe Gorman and Avon. Pictures of this mask's variations can be found in the gallery below.
More information and display of the General Civilian Respirator:
Additional notes: This the filters for this mask and all other British masks from the WW2 era contain Crocidolite also known as "blue asbestos" this form of asbestos is 100 times more dangerous than standard asbestos. To add to the danger of these filters the Arsenic pre filter present on some models is also highly toxic due to Arsenic being a poisonous metal care should be taken when handling this mask and it should be displayed in a closed container. when handling Arsenic components gloves should be worn as well as a Respirator if it is not in a solid state (same applies for the asbestos filter being loose which further encourages use of a Respirator) Wash hands and dispose of gloves after handling.
http://gasmasklexikon.com/ (Johannes' collection)