Not to be a downer on this, but if you're wanting to get this in to Parliament for debate, your petition is missing one major thing:
JUSTIFICATION. And to be honest, simply saying, "Well, the US/Germany/Australia/<insert country here> can do it!" isn't justification.
The big issue here (and I'm going off of 13 years memory here, which was the last time I debated this, and in this forum, now that I think of it) is you are fighting what is now 67 years of precedence, and need to answer why that precedence should be changed. That precedence is the British Telegraphy Act of 1949. To put it very short and sweet, that Act stated that
all communications between two parties are only meant to be heard or shared between those two parties only. Basically, any monitoring or rebroadcasting of those telecommunications by a third party is illegal. It is this last part that is what makes the
rebroadcast of ATC in the UK illegal. You can take a scanner to an airport and listen to them, which is fine; you aren't rebroadcasting it. But the moment you stream it online, you're in trouble.
You will need to justify why that section should be repealed/overturned, and saying that <xxx country> can do it isn't justification for them to overwrite 67 years of precedence.
NOW.....With that said, You may not need to petition Parliament after all.
I did some quick searching through Google and Wikipedia and while I knew that it was updated by the Telegraphy Acts of of 1967 and 1990, I didn't know it parts of it were superseded by the Broadcasting Act of 1984. But The Telegraphy Act of 1949 was fully repealed in 2003.
What you should do is this. Of the signatories in your petition, someone needs to take the lead and write a carefully worded letter and send it OFCOM (both email and written), and state that while you've studied up on all Telegraphy and communications acts from the past 70 years, you currently see nothing in any of those acts that forbid the act of streaming ATC of UK Airports. Seek clarification from that from OFCOM, and explicitly ask them for the ruling, writ of law, all the way down to the wording. You need them to give you the exact words for their justification.
CAVEAT: Quick Wikipedia search for the Wireless Telegraphy Act of 2006 shows Section 48:
http://www.legislation.gov.uk/ukpga/2006/36/part/2/chapter/5You'll need to read through it and re-read through it again, especially sections 46 - 50, to clearly understand it as it relates to ATC streaming, as OFCOM can construe that as 'intercepting'. And that isn't even getting into the main section of it on if this even requires a license.
Regardless, you should also verify that ATC services in the UK are taxpayer funded. If they are, then you may have a right to listen to those services; again, this doesn't provide info on if to provide a feed for those services requires a license. All of those questions are for OFCOM and possibly a telecom lawyer to answer.
BL.