Thanks for the reminder. I did get a reply from David Lee from the Maritime & Coastguard Agency Enforcement Unit.
Here are some excerpts from his emails:
"As you are aware of the Distress Signals and Prevention of Collisions regs, I won't go further on those other that they apply if the signal is fired from, or near a vessel. ('near would come into debate if other vessels were in the vicinity such as busy Solent, Portsmouth Harbour, harbour or coastal areas etc)"
Looking at the Distress Signals and Prevention of Collisions regs I can't find any reference to "near a vessel". He wasn't able to provide a reference for this, so I suspect it may be the normal bluster. I stand to be corrected though.
"I am not a lawyer, but I can say that there have been successful prosecutions that have been made by police forces when flares have been set off inland. These have been offences under the Firearms Act 1968 as pyrotechnics can fall under the definition under s57. Other offences include, wasting police time, breaches of the peace, public disorder, Explosives Substances Act 1874. Each case would have to be looked at on merit and generally will be vigorously pursued."
I'm sure that this is true to some extent, but would be very unlikely to apply to responsible test firing or demo. More bluster.
From his followup email:
"There is no 'specific' legislation, each case would be looked at on merit. With regard to demos etc these are dealt with on a local basis by HM Coastguard MRCCs and Sector Managers. Approved demonstrations are normally with white or green pyros so as not to attract 999 alerts and reports from aircraft.
If anyone was contemplating a demonstration, my advice would be to contact the local MRCC well in advance."
Probably so they can try to tell you that it's illegal!
The MCGA understandably don't like the idea of people firing off distress flares, but done responsibly there shouldn't be any problem. Personally, I would be inclined to follow the procedure as outlined by Doug Stormforce
Just for the record, this is my understanding of the situation but I'm not a lawyer. If you end up in jail it's your own problem!