Reply from Mark Hempsell over on the NASSASpaceflight website
http://forum.nasaspaceflight.com/index.php?topic=30569.0
The constraints of the Explosive Act on the BIS early activities was I think in part due BIS perceptions of the Act which they did not challenge but more due their perception of the state of rocket technology.
The Explosive Act is primarily aimed at public safety although with a consequence it also provided a tool to use against terrorism, which has been a concern for the UK since Victorian times. It does not ban rockets but it does impose a massive bureaucratic burden. . Consider, Pre-war, asking the Secretary of State to provide a licence for large rocket production with the objective to travel between planets and I am sure you will see it would be rather a tough pitch. I doubt the BIS would have successful getting the necessary licence and I don’t think they tried.
I am not a lawyer but my reading of the Act is that, while the Act very clearly and explicitly covers solid propellant rockets, it would not cover liquid rockets. However Pre-war the BIS clearly though liquid rockets were a very long term technology highlighted by the fact the pre-war Moonship was designed around clustered solids. The practical development work they did undertake was all based on the Moonship so if they wanted to do rocket work, then solid rockets would be the only thing they would have thought of and that was covered by the Explosive Act.
However since the Act does cover vaguely “rockets” the BIS may have concluded it would apply to liquids, although of course at the time of drafting the Act this would have had no meaning and almost none of the Acts provision make sense in the context of liquid rocket. The simple expedient of calling liquid rockets “jet engines” (as they were called in the USA) would have overcome this problem by making it clear they were not rockets as defined in the explosives act but that route probably did not occur to them.
So I think the answer to the question why didn’t the BIS do early liquid work pre-war? was due to the BIS members not realising it was a practical proposition. America, Germany and Russia were all keeping their liquid work secret (or more accurately in the case of Goddard in the USA choosing not to publicise it - which was just as effective pre-internet) so they had no way of knowing about the work was going on elsewhere. Post war the BIS did revise the Moonship study around liquids which all the V2 impact sites showed it was clearly an established technology, but also it was clear the field was already way beyond useful amateur efforts on the scale the BIS could muster.
